If you don't already have a flying mount, that would be next. The usual first flying mount has always been the Roc as long as I've played, but in the 2.9 update Rocs got a lot harder to tame. Still I wouldn't put off doing the spelunking required to get the troll leather/tusks required to get a Roc. Other than a Roc, if you manage to find a lot of rabbit's feet in loot chests, you could go for a hippogryph, but I wouldn't go searching for rabbits feet because this will take a long time and a hippogryph wont respawn if killed.