I'm playing a half-elf bard coming up on level 2, and am trying to plan ahead. My plan is to be a lore bard who emphasizes debuffs and control, with the occasional healing word for emergencies (basically only to bring up an ally from unconscious) and stays out of melee when possible. The rest of the party is a monk, a wizard, and a life cleric.
Two things that concern me, though, are (1) relatively weak self-defense capabilities (AC capped at 15, assuming I don't devote an ASI to boost DEX; no shield spell without spending a precious magical secrets slot on it), and (2) few productive ways to use actions while concentrating when low on spell slots and enemies have multiple attacks so that vicious mockery starts to lose its luster.
A level of Hexblade (probably at level 7?) for medium armor and both shield and shield use, a short-rest spell slot, and eldritch blast is an obvious choice. By the time I do that, I'd probably want a second level for agonizing blast and some other invocation; but I don't like the idea of delaying my bard progression that much, and if I wait until high levels, I'm guessing I'll have enough spell slots that I won't need to fall back on attacking often. There's the cleric level (knowledge, maybe?), but it doesn't do much for action-while-concentrating, and I don't have the wisdom for it. But the option I keep coming back to is a single level of Divine Soul (Chaotic) Sorcerer (probably again at Level 7), which gives several goodies:
Access to shield, freeing up a bard slot to take something other than bane, and either another defensive reaction like absorb elements or freeing up a second bard slot by taking healing word as a sorcerer spell.
The Favored by the Gods ability, which seems really strong (I'll hardly ever make an important attack roll, but boosting a failed saving throw once per short rest? Yes please!), and makes me feel more comfortable putting off Resilient (CON) until my CHA is maxed.
Keeping up spell slot progression (compared to Hexblade)
I think either Hexblade or Divine Soul would work, RP-wise. Hexblade gives better passive defense, a better single cantrip, and more 1st level spell use. Divine soul gives more higher level spell use, more useful spells known, more cantrip versatility, and a great class ability. I know it's hard to weigh the relative value of those spell slots without knowing how many short rests to expect in a day. But can anyone comment on the alternatives here? Maybe I'm more worried than I need to be and I'd do just fine with 15 AC and cutting words as long as I stay out of melee... and maybe I'll have enough slots to make good use of my action without needing more cantrips.
Here's what I'm thinking spell selection-wise if I go Divine Soul. If I go Hexblade instead, sub in Eldritch Blast and maybe Armor of Agathys, remove Ray of Frost, Guidance and Sacred Flame, keep Healing Word a Bard spell and remove ... something... maybe regular Invisibility once I get Greater Invis.
Spells by function, level and save type
Sorcerer Spell Magical Secrets Concentration AoE = Area of Effect Tgt = Can select multiple targets
Single Target Debuff/Control/Damage:
L0: Vicious Mockery (WIS), Frostbite (CON), Sacred Flame (DEX), Ray of Frost (Attack) L1: Dissonant Whispers (WIS) L2: Suggestion (WIS), Blindness/Deafness (CON) L3: Enemies Abound (INT) L4: Banishment (CHA) L5: L6: L7: Plane Shift (CHA) L8: Power Word Stun (CON)
I wound up having a conversation with Treantmonk about this over on enworld, and he convinced me that I might be better off just going valor bard to address my defense problem. The biggest cost is level 6 magical secrets, but you keep up your spell progression and can pretty easily get an AC that you can feel pretty comfortable with, even without cutting words and the shield spell. If you're going lore to focus on casting, but then you have to delay spell progression or delay CHA increases to defend yourself, then you're arguably not as good a caster as someone who doesn't have to do that, even if they have access to a couple extra spells known (but no additional slots to use them with). I think if you're in a large or tanky party or you face monsters that don't target back-liners you might just want to stick with Lore and maybe pick up a defensive spell with one of your level 6 picks, but my party is small, and doesn't contain a single d10 or above character (any more), so it's less feasible to just hope to use the tanks as meat shields.
BTW, Treantmonk ended up making an extended video about this a couple months ago, presumably partly inspired by the enworld thread, where he levels up a caster valor bard from 1 to 20, and makes the case.