Your innate magic comes from winter incarnate. It may stem from your bloodline, going back to a time, when frost giants were reigning over your homeland. You may have been blessed; or cursed; with your arcane abilities by a deity of winter, like Auril, The Frostmaiden. It could also be reward for a service that you, or your ancestors provided to a powerful creature. An ancient white dragon perhaps? Whatever the case, your sorcerous origin allows you to conjure and manipulate ice in many ways, potentially being able to transform the lands around you, and to bring about winter itself, wherever you go.

Child of the Cold

At 1st level you are adapted to cold climates, as described in chapter 5 of the Dungeon Master’s Guide. You also know the shape water cantrip.

Aegis of Winter

At 1st level, your innate winter magic can attract ice crystals and have them settle on your body, granting you an extra layer of protection.

At will, you can receive a +2 bonus to your Armor Class and to Dexterity saving throws, whenever there is enough ice within 5 feet of you. You would need an object made of solid ice of at least small size, and alternatively an object or a creature that is covered by ice of at least medium size. Under the right circumstances, weather conditions or other phenomena may suit this purpose as well. The effect ends immediately, if the conditions change; if the source of your ice crystals melts or is shattered.

Cold Affinity

At 6th level, you are more familiar with the effects caused by winter and its ruthlessness, gaining resistance to cold damage.

Ice Barrier

At 6th level, you can conjure a barrier made of ice on water or any solid surface.

As an action, you create a nonmagical pillar of ice within 10 feet of you. You choose a 5-foot-panel on which the pillar bursts into existence, which can be up to 10 feet high.

The barrier is an object that can be damaged and breached. Its AC equals 8 plus your Charisma modifier and it has hit points equal to your sorcerer level plus your Charisma modifier. It is vulnerable to fire damage and is resistent to cold damage.

The barrier melts after 1 minute unless it is destroyed first. It leaves a puddle of water behind. The barrier does not melt, if the temperature is cold enough to keep it frozen. If the barrier cuts through a creature's space when it appears, or if it would trap a creature, it can make a Dexterity saving throw against your spell save DC. On a success, it can move to either side, within 5 feet of the barrier.

You can choose to spend your bonus action as part of the conjuration of your Ice Barrier, to augment its effects:

Frostwall. Add one 5-foot-panel to the barrier for every 1 sorcery point that you are willing to spend. Only one panel has to be within range. A medium sized creature could be trapped by creating a total of four 5-foot-panels, if it fails its Dexterity saving throw.
Ice Spike. If a 5-foot-panel of the barrier is created in the space of a creature, you can spend 2 sorcery points to try and spike it. The creature makes its Dexterity saving throw and it takes 3d6 of magical piercing damage on a failed save, or half as much damage on a successful one. You can increase the damage by 1d6 for every 1 sorcery point that you spend additionally.

You regain the use of this feature after you finish a short rest, or by spending 1 sorcery point as a bonus action.

Winter Step

At 14th level, you learn how to become like a freezing gust of wind that, by spending your bonus action, bounces across the field and into the air. You have to move at least 30 feet but you can arc your movement trajectory up to 90 degrees and change direction once.

You can pass through creatures unhindered and without provoking an attack of opportunity. You have to end your movement in an unoccupied space. Every time you step through a creature, your walking speed is reduced by 10 feet until the end of your next turn, but you may move an additional 10 feet as part of your Winter Step. You can, or might even be forced, to move through the same creature more than once.

You remain able to use this feature by stepping through at least one creature, and otherwise regain an expanded use by completing a long rest.

The Silent Season

At 18th level, you become an avatar of winter.

Choose a spot to remain idle for at least one hour, as you summon the winds of winter. For every hour you spend in this idle, thoughtful state, the temperature around you drops significantly, while clouds begin to thicken in the sky, snowflakes start to fall and exposed water begins to snap freeze. While creatures themselves cannot be frozen or damaged directly, they may suffer from the consequences of the sudden weather changes, e.g. creatures may be trapped underwater after a lake's surface freezes.

Spend 8 hours in idleness, and you may even transform a tropical landscape into a winter wonderland for at least one week, before it starts to slowly return to its normal state.

The effects of this feature may stretch out for up to 5 miles, before they start to slowly fade the further you get away from the center. Depending on how much additional time you spend in your idleness, how often you repeat this behavior, and at your DMs discretion, it may stretch further and even transform an entire landscape. However, it may also be confined to a smaller area, if cast inside a room, a cave, or a functionally similar place, where boundaries can keep the cold from spreading.

While you remain idle, you do not need to eat or sleep, and cannot become exhausted, as your body functions are standing still. But you also do not gain the benefits of a short or long rest during that time.

Finally, for as long as the effects of this feature are active, you automatically gain the benefits of your Aegis of Winter and you may use your Ice Barrier indefinitely, without having to take a rest or by spending sorcery points; you still have to spend sorcery points for its augmentations.