[Andy10v]

If you can get some cheap oem seats or subframes you can strip them down and weld flat bar/box section on to bolt bucket seats onto, lets you adjust them easily. Play with the angle before you weld up fully, my first ones had some silly rake to the bases! Also bolt in so no permanent mods, seat belt buckle is on the subframe on b3/4 so that is sorted as well.

Golf recaro subframes come up for sale more regularly than Audi ones, and can be modified to fit I believe.

If you are fitting a cage you can also just weld bars across with mounting tabs.