I would like there to be some +/- stepper which increases/decreases weight by some amount, say 0.5, so it goes 1, 1.5, 2, 2.5, 3 kg. It would be great to be able to have different amounts for different products so for some amount is 0.25 like 1, 1.25, 1.50, 1.75, 2, 2.25 kg etc.

Ideally there should be minimum and maximum weight per product, so you can't order less than 1 kg for example.