https://youtube.com/@pregnancyandpostpartumtv?feature=shared
Make sure it has an anti burst feature. Also double check the sizing as you need different ones for different heights. I got mine from Argos for maybe like £10. You can just gentle bounce on it and rotate your hips on it as it can help baby get in the right position and it can help you feel more comfortable etc. You can also google specific pregnancy related exercises you can do on them
I ordered one from Amazon for GBP 12. For exercises, there is a YouTube channel - Pregnancy and Postpartum TV. Easy to do exercises and very informative