I’ve spent a lot of research time on this topic. I personally went with 05 Acura RSX seats. I love them, but they are far from a direct fit, and are currently hard mounted to the floor without tracks because the seat risers need to be lowered to accommodate brackets.
the height of the seat base is the biggest factor and depending on your seat selection and body type, you may have to consider a smaller steering wheel.
Pretty much any year Mustang seat can be made to fit. The newer seats may need some modification. Of the Mustang options, I prefer the 2001 Bullitt leather seats, and while originals can be pricey, any SN95 seat (including base V6) can be refoamed and recovered for a pretty reasonable price. Also, they’re available in non-stock colors like white.
For other brands, you’re best off looking at 2 door sporty cars, both for their general size and fold-forward feature. Fiero seats have been a favorite for years because they’re slim and a direct fit. I personally have been eyeing Audi TT seats for my 64.5 coupe. They made them for a long time and are available in quite a large variety of styles.
Here are the Acura seats in my 66: