Bike Fit London/Home Counties

[bigdom]

I'm making an concerted effort this year to do more cycling. Whilst I appreciate I'm still in the minor leagues, my weekly average is now up to around 140 miles and i'm experiencing a few issues. Mainly lower back pain (old injury) and comfort on the seat, this one, is a pain in the arse once beyond 20/25 miles. I've tried a few different seats, positions, angles and it hasn't made much difference; so I'm assuming it's possibly overall fit.

Being on the M3/M25 corridor, and reading some old threads, I see I have a few options pretty close.

Bike Whisperer
Sigma (includes seat pressure mapping)
Vankru

Anyone used any, have any recommendations?

Thanks