IVF Newbie and need some help please - from the UK

Hello all,

I'm 37 and have two boys, we would like a 3rd but dearly would love a girl which would be our final child. Would any be able to recommend a good clinic to get in touch with? Would you recommend mircosort ( given my age?) Can you have pretests at local GPs or would it involve going to London?
Any idea of costs would be great too.
I've been trying to do some research but i'm feeling a bit overwhelmed by all the info and then end up reading posts instead!

Thank you in advance for your help