Such a simple yet tricky question.
I'd have webbing and tentacle constrictions mimic the clothe binding mechanics. You'd click on the equip slot you want to constrict, which pulls up a menu regardless of if an item's occupying it. In the third row I'd place the option to constrict the part. It would then appear blocked similar to if another piece of clothing were blocking it. Depending on what's bound, some secondary slots are also bound (eg. binding your eyes or hair also binds your head). To prevent multiple turns of individually blocking equip slots, I'd have options to constrict the lower body (legs, tail, hips) or upper body (arms, chest, wings, head). Muscle control options should always be available. A bit clunky, but it could work.
As for knotting, you could simply prevent pulling out for non-elastic orifices, forcing you to stay fucking for however long it takes to go down (10-20 in game minutes by default, adjustable in settings). You and the partner you're stuck to could still perform other actions and nothing stopping a third partner from going to town on your free parts. Ripping out a bulbous dick prematurely would be a sadistic/masochistic action.