Amanda
God luck with seed saving. I have trying a few. Tomato, chilli, pepper, pea, broad bean, dwarf bean and French bean are dead easy. Onion worked OK but it is a two year cycle. This year I will try lettuce, winter radish.
Space is an issue if you have a small growing space. Pea and bean create good seeds n a pot, but I wonder if there eould be effects if you grew peas 5 years in a row not in the ground.