I removed all the copper wire from the old seat pad and cut where it overlapped the side bolster, the material is only about 2mm thick so I don’t think your bum will notice, trying to peel the old pad off was a total pain and in places took large chunks of foam out (that had to be glued back in again)
when I had finished and the new heated pad was installed felt the same as before and same as the passenger one and was very hot,
side note when I removed the seat cover I could see that the element was broken on the offside bolster I could of repaired it but the time taken to get to get that point and the broken finger nails for the cost of the replacement seat pad I didn’t bother!