Check out Schleich, Papo, etc. They make accurate toy models of real-world snakes, lizards, bats, etc., which can be adapted to gaming. Best part is, they come with a decent factory paint job which needs little enhancement! Amazon.uk is a great place to look.
I bought a bunch of small, Schleich, lizard toys, which I am using as mounts for Lizard Men figures, to create monstrous cavalry. I have plastic Lizard Men figures, so after I cut off their molded base, I just used some E6000 Glue to attach them to the Lizards' necks. The Lizard Men ride 'em bareback. No painting required, but I applied The Dip to the Lizards, and it improved their appearance for my purposes, quite nicely.
I also picked up some Schleich Fruit Bat toys, to serve as aerial mounts for Goblins. I Hot Glue'd a stick pin to the base, then I bent the shaft 90-degrees, and pushed the sharp point into the toy Bats. This allows me to rotate (bank) the bats on the pins. The Goblin figures wrap their legs around the Bat's neck -- a little E6000 Glue, and done. Cheers!