My Bullitt cargo bike has Wellgo studded pedals. They are terrific and if you're going clipless-free, then something like that will give you the best grip. I liked them so much that I decided to get a SPD/studded platform pedal for my CX bike (Wellgo WAM-D10, $40). I ride the bike on the platform side around town and on the SPD side for workouts and longer commutes and it works great both ways. You could go that route and it would leave your options open if you later decide to go back and/or find shoes that work.