I would recommend Karen Wykes. Not quite as lental-weaverish as Karel Ironside. Karen used to do classes in both Brighton and Hove, day ones and eve ones. She is a little scatty, but very good. I loved doing her classes! She has had natiral births and a c-section, so is quite rounded in her views of the whole thing. I personally found Karel's classes a bit too hippy-ish - and don't ever mention the word MMR in her presence...
I believe there are also yoga classes attached to Sure Start centres, but don't quote me on that.
Best of luck. Brighton is a good place for these sorts of things. You could also try doing the aqua natal classes at the Price Regent - I always found those quite friendly and good for keeping active.
I run a pregnancy yoga course in Hove. We focus on stretching out the body in specific areas to allow for the changes in your body. You will also learn breathing techniques to help you through labour and to help you as your baby bump grows and reduces your lung capacity.
It's a friendly environment and I myself am pregnant so can understand the changes you are experiencing mentally, physically and emotionally.
If you are interested you can email me at firstname.lastname@example.org or go to my website for more information