if you don't regularly or ever use the back seat area, I had a good experience with Acura Integra seats. You need to make brackets and they crowd the handbrake but are very comfortable and supportive.  I think mine came from a late 80's- or early 90's model. 
I put a square tube across the front and welded 'ears' to let them sit in the front mounts.  Using the same 1" square tubing, I made legs for the back of the seat with a plate on the bottom of the legs to dispurse the weight on the floor pan.

If you do decide to go with reupholstery, or are trying out different seats - don't make the mistake of going for seats that have soft cushions and padding.

These may seem very comfortable on the initial sit down, but they don't support the muscles and joints very well. Before too long you'll feel the aches and pain. Get seats that are firm, maybe even on the hard side. They'll provide better support and long term comfort, provided the seat is shaped well.

I found a set of first gen Mazda Miata/MX5 seats on craigslist and installed them myself. You'll have to make or have made brackets to mount them. I really like the fit and ride; I'm 6'1" and right now about 250lbs. Super comfortable; we just did a run down the coast on California Hwy1 with the club (MOASF) and survived!

I've owned and enjoyed driving my Mini for 18 years now but the last couple years have been less fun. I'm now 86 with bad back and a spinal stimulator implant to ease the discomfort from worn out seats in the Mini. It's either rebuild existing seats with a kit from Newton or try Corbeau seats which look the most promising. Does anyone have any suggestions or experience in switching seats and will there be an improvement in the ride. Any advise will be appreciated.