I would say duergar seem appropriate even though they're not officially a part of it, Dark Sun seems really iffy about dungeons, caverns, etc. I can't really tell if its intentionally an anti dungeon world or what.
Thri kreen as a race are easy, their MM statblock looks clearly intended to be in line with a future PC incarnation.
Natural AC 13 (the standard for natural armor races),
Ability mods same as in 2e; they're clearly in the orc/kobold/etc. camp), and their stats look like they reflect +2 dex, +1 wis, -1 int, -2 cha.
Natural weapons are Claws and bite per MM entry. They don't get quadra-slash anymore unfortunately, 2d4+str claws, 1d6+str bite, con save that is 8+proficiency+con mod or be poisoned for 1 minute; failure by 5+ causes paralysis. You can give them the bite at level 5, or you may wish to analyze the power level. You may wish to give them a bonus action bite at the same time they get it in 2e, perhaps only when attacking with claws.
Standing Leap, Chameleon Carapace as MM entry.
(Optional) Subraces
Jeral: +1 con, martial weapon proficiency with chatkcha.
Tok'sa: +1 str, martial weapon proficiency with gythka.
You may wish to let them take a bonus action attack with a kreen weapon when wielding only kreen weapons and no shield, and perhaps as long as they are using two or more kreen weapons. This would be a high power level element, but its not gonna be stacked with shield bashing or polearm mastery, so it may be alright.
Finally, you may wish to give them psionics per the MM entry, parceled out across a few levels like yuan ti.
The result would probably be a high power race, but still probably weaker than vhuman, aasimar or pureblood.
Please note that this isn't my attempt to make a thri kreen race based off what I think it should be, but the most faithful conversion from the monster manual entry I can get that might approach balance.
