If you are puttering around then a slatted floor will do. The smallest motor eg 2hp Suzuki will drive you at hull speed too. I personally would avoid the 2 hp aircooled Honda as it is noisy.
If you want a planing dink then an inflateable floor that gives it a V profile is the way to go. Something like this CLICKY
You will need at least 8 hp and 9.9 or 15 hp if the boat is rated for it is better. Try to find a used 2 stroke Yamaha if you can. Tohatsu Evinrude and Johnsons are OK. I am not a Mercury fan. Check out the weight of the OB, sometimes the 15hp weighs less than the 8hp.