BTW price is the most important. I got my 5/3 suit on a price of 180 euro. That's a fair price! The fusion would cost round about 119 euro. That's not so cheap...
Where to buy? In any surf shop I think.
Internet is an option, but you should try it on, so it's a bit more difficult! Unless you can try a harness/suit from a friend first.
Best prices? No idea... Would like to know!
If you find the seat cheaper, send me a mail on email@example.com
(I'm not from the UK as my address might suggest!)