Hey Shrink,
Have a look at my other post re roll bar that supports existing seat belts: NC mods Part 1 - Roll bar and coilovers
You’ll notice there are fixing on it for the original seat belts. Was an optional extra but well worth it as gives you the option of using either belt or harness.
I will soon be looking for bucket seats - first track day in 3 weeks time and no doubt the lack of support in my current seats will be an issue.
IF removal of factory fitted side airbags is an MOT failure then you could just keep your old seat and bolt it back in for its MOT?
As for seats I think you really need to sit in them to try them out.
These seem quite popular but look way to upright to be comfortable?
These guys were at the MX5 show last month and I tried out their seat:
Really comfortable! BUT probably 2-3 times the price of the Sparco. The one at the car show was a prototype but they reckon they should go in to production this month…