What is the motor? If you really mean 12V/80W then that is less than 7A. If you only need to control speed and not direction then you just want an N-channel logic-level MOSFET and there are many that can handle that sort of current. I've used STP36NF06L and FDB7030BL which are both reasonably priced but there are loads of other possibilities. I'd look for at least 30V and 30A because you want some headroom.
Steve