To be honest, I suggest you leave any thoughts of foot retention alone for the moment.

Many riders have a natural tendency to ride toe-in or toe-out, and trying to artificially correct that with clips-and-straps or clipless might lead to trouble you don't need at the moment. In fact, most riders with toe-in or toe-out ride that way even with clipless pedals.

Get used to riding the bike at a higher cadence first on platform pedals. One of the tendencies for people either new to the game, or coming back, is that they want a fast progression.

Take it easy, and change things one at a time after you have spent time with the current set-up.

You might consider using a pair of shoes with a harder, less flexible sole, however.