It is developing into a campaign. Players want to start out as Thelitian slaves escaping/ being sent on a mission they probably won't come back from by an especially evil master.
Would it work to place a feline or canine based race somewhere? Can be another continent. Basically, the mission I have in mind is to find out where one unique slave comes from so they can get more. Could also be some sort of underground race (especially considering a few of the players want to go on a drow killing spree).
Very cool! Glad you and your players like it enough to give it a whirl.
I created the Jerali (felinoids a la the Thundercats, but without the tech

who inhabit the northern edge of the desert and the orean plains north of Thelitian. You could very easily use stats for a tabaxi or rakasta for them.
But there's no reason you couldn't use/there wouldn't be prides of Wemic, were-panthers, some desert-based nomadic tabaxi or rakastas if you like. I personally, do not use/have "shifters" in the game, but if you like 'em, no reason there couldn't be some small localized tribe of feline-shifters wandering the desert borders.
Feline or Canine humanoids would probably be quite exotic and, thus, highly prized as slaves to the Thelitians...especially/possibly as exotic combatants for their gladiatorial blood-games.
Basically any race that would be "rare" to find in the desert (which would be any non-thelitian human or humanoid) would be prized by the Thelitians -the huge blond northern barbarian tribesmen from Gorunduu, the dark-skinned Tanku islanders, elves (probably moreso for house slaves or sex-toys than gladiators, but it's your campaign), 'taurs of all sorts, any "underground race" you like (except Drow as drow do not exist in the surface world's knowledge), even a dwarf who was decked out for the arena as some "warrior of the mountains" or kept chained to some noble's forge as their "master smith" is uncommon if not rare in the desert- all would be valuable "possessions" in the Thelitians' eyes.
Sounds like a great way to start the game!
PS: to get to the Underworld/-dark for some drow-killin', obviously you could plop in a cave or cavern anywhere that sinks down far enough. But the obvious choices would be to try to get out of the desert and find some entry in the Daegun mountains (passed/around the dwarf kingdom that exists in the southern portion of the range. The northern part of the range is rife with all kinds of giants, rock trolls and other nasty beasties) or head west-northwest toward the evil cursed broken lands of Thole (full of "Grorn" -Orea's gnolls, basically, but more wolf-/jackalesque than hyena, orcs, and all manner of evil and monster), where an access to the Underdark undoubtedly is, as well as gateways to even
less savory places.
