A few build options for you:

1) MC into Battlemaster - this gives you 4 superiority dice which you can use for a variety of things in combo with your sneak attack. If you go up to level 5 you get extra attack which gives you more options of what to do in combat.

2) Dip 1 level into Fighter then take the Shield Master feat and grab Expertise in Athletics - this gives you a BA shove as well as more damage and AC

3) Take the Healer feat - this gives you a non-magic ability to heal and let's you play as a battle-field medic as needed.

4) Take Magic Initiate to get Find Familiar - this gives you a whole extra turn in combat from your familiar which you can use to do a variety of things.

5) Use two-weapon fighting - that BA attack doubles your chance to hit and deal sneak attack damage meaning you're far less likely to waste a turn.

6) Give up on being a rogue in combat and instead MC as a full spellcaster.

Options 1, 4 and 5 are most likely what I'm gonna do. 

Quote from CrimsonCrow17 >>

Options 1, 4 and 5 are most likely what I'm gonna do. 

I can vouch for 5 -- I'm playing an MC zealot barb 8/swashbuckler4 (and now battle master 4 deeper into the campaign), and getting up to three attacks per turn to ensure Sneak/Divine Fury goes off is huge

You could take 2 levels of paladin if your STR is high enough to get compelled duel, which functions well with Swashbuckler’s sneak attack.

My Strength score is 8 and I'm not wasting the amount of ASI it would take to bring it to 13 for the requirement.

Then probably do one of the other suggestions 

Quote from MonksAreGreat70 >>

You could take 2 levels of paladin if your STR is high enough to get compelled duel, which functions well with Swashbuckler’s sneak attack.

 
You could pick that up with the fey touched feat

both thematically and functionally, I would recommend fathomless warlock, or any warlock. you can get pact of the blade to get a melee weapon, and it sort of fits the whole swashbuckler thing. I saw you were thinking hexblade too, that would also work

Reckless attack only works with STR attacks

Whoops. Guess I read “use a finesse or ranged weapon” as “use DEX”. Probably doesn’t help that I was reading the Monk UA this morning. 

I’m late to the game, but I’d go 4 levels College of Swords Bard for the added versatility and it thematically fits the swashbuckler vibe. Two weapon fighting style is great for a melee class that wants the offhand attack to ensure a hit for sneak attack. The Blade Flourish options can give a handy defense, AOE, or control option. Bards also have some handy 1st and 2nd level spells. The extra expertise is nice too. 

edit: I’d also pick up Magic Initiate Sorcerer for Green Flame Blade, Booming Blade and Shield. 

Multi into Fighter or Ranger for the fighting style, weapon and armor proficiencies.

3 levels of Fighter would get you Second Wind, Action Surge and crit on a 19+.

3 levels of Ranger would get you additional +2d6 or 1d6+1d8 damage depending, once per turn.

1 Level of War Cleric gets you weapon and armor proficiencies, and Divine Favor. 

Check out swords bard. You can greatly enhance your fighting and defense with swords bards version of bardic inspiration. 

If you want to go deep into CHA min-maxing with Panache, try Fey Wanderer Ranger.

It can get pretty crazy if you do it right.

I can't really think of a thematic reason why he'd go ranger. The campaign doesn't really have anything to do with the fey wild and no PC of NPC has any connection to the fey wild.

He usually uses a rapier and if he dual wields then he can't cast spells unless he takes the War Caster feat, but I don't want to spend too many ASI on Feats

Quote from CrimsonCrow17 >>

He usually uses a rapier and if he dual wields then he can't cast spells unless he takes the War Caster feat, but I don't want to spend too many ASI on Feats

 You can if you go Eldritch Knight.

His INT is an 8

Fey Touched only increases Charisma, Intelligence or Wisdom scores by 1. It does nothing for the physical stats like Strength, Dexterity or Constitution. Also, thanks to some in game shenanigans my rogue has a 35ft movement speed, combines with fancy footwork I can get out of a 1v1 situation without using a bonus action or a leveled spell. For crowds I could just disengage as a BA. I did consider taking Fey Touched, but looking at it I saw it was kind of a waste since the only spells I could pick from the list were either divination or enchantment. Not exactly combat based spells and the ones that were had the Concentration tag to them.

Quote from CrimsonCrow17 >>

Fey Touched only increases Charisma, Intelligence or Wisdom scores by 1. It does nothing for the physical stats like Strength, Dexterity or Constitution. Also, thanks to some in game shenanigans my rogue has a 35ft movement speed, combines with fancy footwork I can get out of a 1v1 situation without using a bonus action or a leveled spell. For crowds I could just disengage as a BA. I did consider taking Fey Touched, but looking at it I saw it was kind of a waste since the only spells I could pick from the list were either divination or enchantment. Not exactly combat based spells and the ones that were had the Concentration tag to them.

 
The only reason I mentioned the Fey Touched feat was as an alternate to taking a 2 level dip into Paladin to pick up access to compelled duel, which someone else had mentioned.