Im going through the same thing and posted recently... i actually put the change mat on the floor...she still rolls over and crawls away but i know she is safe.

I put her down and get stuff ready. bring her back and quickly change her, sometimes i put my leg on the side to try slow her down when she rolls over.

I sit her in my lap to dress her and she cant really roll around... this will work until she learns how to get up then back to the drawing board.

Goodluck