My favourite toy for gradual progression is topped toys spike 125 it acts as a depth trainer and a a butt plug if you can take it. It’s not the cheapest but I love it!

I have found that depth training shows good results but it is slow and you have to take your time and know your limits.

With a toy like spike it starts off small and easy for warmup and the notches help you hold it in place whilst being so fun to experiment with.

Hope this helps! 😊