Party Synergies for Melee Rogue with Sentinel

Question

I'm playing a melee rogue (Arcane Trickster). I'm looking to multiply my sneak attack damage by taking the Sentinel feat to increase the odds of getting to make attacks on someone else's turn.

Pro: When I make an out-of-turn attack, with advantage or a nearby party member, I do a lot more damage than the Sentinel attack normally does.

Con: I'm pretty squishy; with 20 Dex and Studded Leather, I'm AC 17, significantly lower than the typical tank, which means enemies have comparatively little reason to attack someone else or run away (well, the many sources of advantage I collect to ensure sneak attack might make them run away eventually, but until then, I'm definitely the softest frontliner in the party, both on AC and HP).

My goal: Find some way for my fellow front-liners to make themselves fatter targets despite being less dangerous, harder to hit, and tougher. They can't use Sentinel (which synergizes poorly with itself; if all of us have Sentinel, the special attack for attacking someone else without Sentinel never occurs, so a third of the feat is wasted). Obviously I can do other stuff to help eventually (multiclass Bladesinger to boost my AC, get magic armor, get a fighting style through multiclassing or Fighting Initiate, etc.), but all of those will take awhile to come online (my Int is only 14, so even Bladesinger would only bump my AC by 2, and slow my Rogue advancement by two levels).

So my question is: What class features, spells, magic items, etc. could other party members take/learn/acquire to get tank features (defined as "anything that penalizes or punishes an opponent for attacking me instead of them") that would take the heat off me, a squishy Rogue who is staying in melee range? Ideally passive abilities that stack (where multiple abilities that require your reaction are effectively "Choose one").

We stumbled on one option by accident; the party Armorer Artificer's Thunder Gauntlets mean that, assuming they hit, their target will have Disadvantage on attacks against me (enough to make it meaningfully harder to hit my AC 17 than their AC 20). Originally I'd planned to take Mobile instead of Sentinel and retreat to cover/hide between turns, but with that disadvantage alone (plus a party full of casters who can force rerolling successful attacks, for effectively triple disadvantage), he can protect me enough to make the extra Sneak Attack damage attractive. Are there other things (especially things that can stack with Thunder Gauntlets, but any source of "attack no one but the tank" is useful) that would have similar synergy with a Sentinel Rogue?

Current party make-up

• Arcane Trickster 5 (Wood Elf)
• Armorer Artificer 5 (Plasmoid)
• College of Spirits Bard 5 (Owlin)
• Chronurgy Wizard (Fairy)

The non-frontliners are really off the frontline (damn flying PCs) so I'm totally dependent on the Armorer as the tank to draw attacks off me (though I plan to pick Mirror Image soon, and between Uncanny Dodge and Silvery Barbs I can defend myself a bit if they decide to attack me anyway). We're all level 5, this is planning ahead for level 8, so multiclassing is a possibility.

Answer 1

Disguise Self

Nearly everyone in your party should be able to cast this if they want, not only your team mates, also you. And all of you can look very different from how you are actually armored. The tanky armor Artificer? Looks like a flimsy rogue elf now. You? Clearly wearing full plate, to all appearances. It's not a crunchy mechanical approach, but our rogue has used it with good success — obviously there are other good uses for it, too.

There are a few downsides: it depends a bit on how your DM handles it when they get hit by weapons, and the duration of only one hour means you cannot all have this up all the time, but it's good enough for an extended sortie.

Answer 2

There's the "protection" fighting style

A fighter (or a paladin, or someone with the Fighting Initiate feat) can take the "protection" fighting style, which lets them spend their reaction to give disadvantage to someone attacking an ally, if the ally is within five feet. They must be wielding a shield.

In most cases, this is not particularly good mechanically: reactions are precious, and the aoo granted by the Sentinel feat is just better. I would hesitate to ask another player at the table to spend their resources picking up this feat just to protect my character. But this does seem to be the sort of thing you're asking for, and it has a decent interaction with Sentinel.

Your allies can deliberately provoke attacks

If the artificer stands next to you and then walks away, he will provoke attacks from anyone in front of you. The rules say that this attack occurs "right before [the artificer] leaves [the enemy's] reach", meaning that the artificer still counts as being next to you for purposes of your sneak attack.

There's synergy with the battlemaster fighter's commander's-strike maneuver

...but it's probably not worth trying to get your allies to pick up three levels of fighter to enable. If you got a new party member, it might be worth mentioning this to them.

You could get someone to pick up the Martial Adept feat, which gives one use of that maneuver per short rest, but honestly that still doesn't seem super worth it.

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There's also the artificer's Thunder Gauntlets, as you mentioned. Your question indicates you already know about this, but I'm including it here for completeness.