Would be relatively easy, you need to get a 24v power supply and a contactor with a 24v coil. and a box to mount it in safely.
It’s not much different than the isolation relay diagram I have made for aquastat systems, with the exception that you should really use a contactor, not a relay, and you should make sure that any wires you use on the high voltage side can handle the amps. Baseboard heaters are relatively safe to control with a contactor as they use convection and don’t rely on a fan to keep the element from burning up.