Getting the valuations isn't so you have an idea of what it's worth though. It's so you can email him telling him,
I have arranged valuations on our property, the results os which are:
Estate Agent 1 £x
Estate Agent 2 £x
Estate Agent 3 £x
etc
Which is a) action on your part, improving your mh; b) informing him that you are acting regardless of his inaction.
This, I hope, would show him that he really doesn't have you in a stranglehold, that you are a free agent who can make decisions for yourself.
Or, you could have the valuations done and sit on them for a while; just knowing you've done it in spite of his efforts to shut you down will improve your outlook. You're going to have to have them done at some point anyway, why not now?