Are leather seats firm for back support/back problems

I have a 10 year old toyota camry and am now buying a new car. I have had a L4/L5 back problem but it is generally now pain free. I do need good support however.

with leather seats in many cars, how can I find out how firm the leather seats will be over the long haul, more than just a test drive?

Leather is just the outerskin and has nothing to with the comfort and construction of seat.

Agreed, the leather has nothing to do with it and it’s all in the seat design.
Some seats have inflatable bladders in them for lumbar support but generally these screw up after a while and leak off. It becomes an aggravation to keep hitting the button.

There are some add-on lumbar supports that are sold or possibly an auto upholstery shop could add some additional padding to the seat back.
I know all about this subject unfortunately; L2-L5, T2-T3, and C3 problems.