They new Smith and Wesson combat lights are very nice. They use 2 lithium cells and fit a 1" mount. they gave my company a handfull as samples and I put one on my AR. It works very well and does not weight down the rifle. They also have a mount for it.
Your idea of using a tail cap button vs the presure pad is a lot better for a battle/CQB rifle, no wires to hang up on stuf an break.
I have used standard scope mounts to mount 1" flash lights also.