If you are already going to level ten Pally then go for Pally 11 and get +1d8 radiant damage to every attack you make. That is much better than an extra action once every short reest and another fighting style while giving up the level 12 feat.
If you want to multi I'd look to jump at level two when you get smite or level six is good where you get the aura of protection.
The usual suspects for Pally multi are Bard, Sorcerer, Warlock as theses are all full spell casters and Cha based makes for lots of smites from lots of spell slots. Level 5 Warlock pact of the Blade gets you SAD and three attacks instead of two.
Barbarian gets you Reckless Attack at level 2 for easier hitting and rage is nice but it limits you to medium armour. Fighter level 6 gets you two feats, another fighting style, action surge and either spells, manoevers or more crits. Could go Pally 8/Barb 2/Fighter 2; Pally 6/Barb 6; Pally 6/Barb 2/Rogue Thief 4.
The possibilites are immense but ditching Pally after ten levels seems like a poor choice.
