We were exactly the same SJ (bit different in the technical aspects of course...) but the same in that we were way to scared to do anything that might loosen little Bubble's grip in there!

I think if you're not comfy with doing it then don't. Besides, the times we started it usually ended pretty quickly as I just wasn't into it - all I could think was "what about Bubble".
(Though to be honest I was constantly exhausted until about 10 weeks, so sex was the last thing I wanted to do when I hopped into bed anyway!!!)