Clavote;
I am a new member to this site (but have viewed it for a long time now) and there are lots of climbers on here who have climbed longer and higher than I ever will, so I would certainly listen to their recommendations over mine, ergo...
I would stick with your tent. It sounds like you love it, and you should never give up what has worked for you, trust me. My first bivy experience in 1998 proved it. I borrowed a 'roomy' Bibler Tripod over my much loved 4 season mountaineering tent and I was caught in a sudden white out on Mt. Constance (in the Olympics) and had to spend 6 hours holed up in it. In this case, however, a tent wouldn't have been much use to me on the small spot I found myself trapped upon. I thought I would die without being able to move around. Bivys are great for summer, but not if inclement weather is threatening.
As for the pad dilemma, it depends on the size/spec of the pad vs. specs of bivy, vs. girth of human. I can't use my pad in the REI minimalist bivy, but it fits well in the Bibler Tripod and the Black Diamond Lightsabre. Those two bivies have more foot room clearance for a pad. (Note, in cold weather, your bivy will have condensation). No matter what shelter I carry, I always have a small sil-tarp with me, so I put my pad on that when used under the bivy. If you aren't on a level spot you might slide off the pad if it isn't inside the bivy, though. But I toss and turn a lot, which makes it worse. Perhaps someone will let you borrow their gear to try it out before you buy. I say buy a bivy that you like, but only use it in good weather when the the biting mozzies are at a minimum. I hike/backpack/cycle tour a lot too, and I always have the lightweight bivy along...if not for me, for someone else I may find hurt or needy on the trail.
Good luck...
joeschmoe