How to control an automatic transmission?

So I want to make a car with a few friends and we want to install an automatic transmission (something like a zf 8hp or similar, maybe a dct) but I haven't been able to understand how you are supposed to control this, I don't mean making a controller from the ground up, I just want something that goes on the transmission and controls the shifts (maybe some high end ecus already have a controller?) Any advice is welcome (and if it's affordable, better, but something tells me that automatic transmission and affordability doesn't really mix)