bicycle seat that won't hurt my bottom

I've been cycling off and on for nearly a year. When I started, I'd ride
about 8 miles and didn't have much, if any, of my bottom hurting. Now that
I'm doubling the distance, lately my bottom has been hurting a little more
and I wonder if I could change the seat to something better. I'm overweight
by about 40 lbs, so that doesn't help when sitting on a small seat. One
time I had a pilonidal cyst removed from my bottom and the irritation I'm
getting is appearing in that area and I don't want to agitate it any
further.

So, recommendations for a seat would be appreciated.

Thanks,
Bill