My DD had been a beautiful sleeper (mostly in her own cot) up until about this age too! My pet peeve was that her disruptions started right in winter time and I froze trying to re-settle her in her own bed. So she came in to us, but same as you, sometimes the constant thrashing about meant we had to take her out and try the cot again. Our solution might not work for you, but here's what we did:

I took the sides off her cot to turn it into the junior bed. She then had the freedom to jump out of bed and run into our bedroom when she needed us. No more getting up in the cold for me! I was worried she would fall over or run into something in the dark, but no, she belted in at full pace the first night without any light at all! Because she knew she was able to come into us I think it made it easier for her too. Maybe because I didn't have to get out of bed I just looked at it differently. I think she started doing it less and less though. And we got a bit firm, you must sleep in bed with Mummy and Daddy, any playing and jumping around and you can go back in your own bed. In the morning she's also able to get up and play if she wants to.

Don't know if it will help you, but it made life easier for us.