If you want good defenses on any build you sprinkle single level of monk and 2 levels of paladin on it. Here are some examples
Scaled Fist 1/ Paladin 3/ Knife Master Rogue 4/ Slayer 12
This is a dex based crit fisher build. You turn into a blender and you deal a lot of damage with sneak attacks and crits, also your crits fuel outflank and sieze the moment procs for your other melee characters.
Scaled Fist 1/ Paladin 3/ Two Handed Fighter 16
You have acess to best monk robe (+5 dodge bonus to AC), cha to AC (from monk), cha to saves (from paladin 2, this is default cut off point from paladin), immunity to diseases and fear (from paladin 3, not necessary but I like it). Until you get stat boosting items you rock that fullplate armour, then you switch to robes (yes even with a STR based character) for much higher AC. It is a very simple build, you hit and stuff dies.
Scaled Fist 1/ Paladin 3/ Bard 2 (Archaeologist for uncanny dodge probably)/ Dragon Disciple 4/ Two Handed Fighter 10
A variant of previous build. Extra STR, bite attack, and natural armour from Dragon Disciple. Access to mirror image thanks to bard casting.
Scaled Fist 1/ Paladin 3/ Fighter 2/ Rogue 4/ Duelist 10
If you want a low maintenance character with highest defenses try this. If something can hit this run.
Monk (Scaled fist if you want CHA focus instead of WIS) 1/ Sword Saint 19
Lower saves because no divine grace from Paladin but high AC becomes online much earlier. It crits really really hard. Also has access to Mirror Image. You can also kill swarm with this (not on early game) if you slap several elemental weapon enchantments to your weapon with Arcane Pool easily. You can be STR or DEX based depending on your preference.
Note: Dex builds inherently have higher defenses thanks to higher touch AC. STR based characters will have higher damage potential because size increase.
I am not sure how you'll deal with some of the monsters like the swarms in melee
If your weapon have any elemental damage enchantment you can still deal damage to them. Torches also work. Or you can just use Jubilost. He obliterates them.