I did the same thing. At first, I used some rubbery Halloween toy bats. They were too toy-like, and very flimsy. I upgraded to medium-hard plastic, Schleich Fruit Bats: perfect size, no painting required! Unfortunately, they're now OOP.
I am using Caesar 1/72 Goblin figures, which when used with 25-28mm Humans, match up to the proper proportions, per Gygax's 1977 AD&D Monster Manual sizes. I cut the figure's feet off the molded base, and then I used E6000 Glue to attach them around the Bat's neck. I discovered I do need to cut a notch in the Bat's neck, both sides, to allow the Goblin figures to stay put, even with the Glue!
I did play one game with the rubbery Bat Cavalry. It was really impressive to see a cloud of Goblin Bat Cavalry enveloping Human Infantry on the ground! Loads of fun!
I used 2"-square MDF bases, with a 2"-long quilting pin, to hold the Bats upright. The pin has a 1/8" round plastic head, which I Hot Glued to the base. I bent the sharp tip 90-degrees, pushing it into the underbelly of the Bats -- good thing I couldn't hear them yelp!
By mounting them on a bent pin tip, I can bank them on their stands, so no two are flying exactly the same, just as you would expect with a swarm of Bats!
They are not terribly effective in combat, but… Wow! They have tremendous visual impact on the table! Loads of fun! Good luck with your Goblin Bat Cavalry! Cheers!
