Leather interior upgrades, what else will fit, if any?

[Chuck_morris]

I was debating selling my 06 3.0d M-Sport but I can't bare to see it go. It's an awesome car but has some things which annoy me. The driver's seat is uncomfortable as hell and really has a negative effect on my back.

I was told that E46 M3 seats will fit in there so was thinking just find two front seats from an M3 and throw them in but what would be even cooler would be if an interior of a newer BMW would fit in there?

Obviously technology, wireing and such has come along way so I'd imagine it's no way as easy as throwing them in but I'd like to see if anyone else has done something similar.

Thanks in advance.

Chuck in the grey misrible UK.