Nik,
How long have you been shooting a SG?
Only reason I ask is the first few times I put a box or two of cartridges through one I was sore but I have since learnt this was down to not mounting the gun correctly rather than recoil.
Like you I'm only 12 stone but 6' tall, so built like a snake.
My preference is Berettas with 32" barrels, no idea why it's just what suits me.
What ever you buy make sure your gun shop will let you take it back within 7 days if it doesn't suit you, most shops will do this if you ask.
ATB,
Mick.