Hey lem496, yes I understand this can be a tricky situation. Does your coach now and the new coach both work at the same club? Because if not you could always say that you aren’t going to continue 1-1 coaching because of costs or time etc. And then start with new coach, basically just a small white lie.
However if you aren’t comfortable with this or if they coach at the same club and the old coach will see you with the new one then the best solution is probably pure honesty and say that you would like to experiment and try a new coach. It sounds like you are committed to improving and playing a lot so you definitely want to get the best coach possible to make the most of your time. I’m sure they wilk understand and any arkwardness won’t last.