Hello, I'm collecting seeds from my plants for next year too. I agree, keep checking the plants and the seed pots, let them dry out naturally. Collect the seed/seed head in a paper bag and dry them out further. For me I would sow them quite soon after collecting if they are ready.
Foxgloves & poppies have thousand of seeds. My foxgloves seeds are ready now there is going to be so many of them. I plan to snip off the plants and shake it around, and I will still be able to grow some from seed as well.
I collected some seeds of my ragged robin a few weeks ago and sowed them........I've got quite few seedlings coming through.
Let the seed heads get really dry and ready to burst, or just opening,and then shake them out into a bag. I store mine in those little individual jam pots you get in hotels. Do make sure they are really ripe and dry before you store or they will get mildewy. Pansy seeds can be picked when well swollen and left in a jam jar on a sunny windowsill to dry put and burst open - I never buy new seed unless I want a specific colour that I don't have. I often just sprinkle seed back into the pots or areas where they were growing.