For swimming, I use the silicone ones - to keep water out of my ears not to reduce noise. You can mold them into any shape and size you like, and only a small amount goes into the ear canal. I do get the children's size ones, but if you have the "adult" size silicone you can just tear off however much material you need.

I historically did buy earplugs in the 200-pair boxes. DH still does. If I find something I can tolerate better than the SparkPlugs I have a box of now, I'll buy a box of those. Even if only one person in the household is using them, if you use them often you'll use them up plenty fast - they're only good for maybe 30-40 hours on the outside IME. Beyond that, depending on the type, they might get impossible to roll up and insert, or they just stop blocking sound. Or if you're prone to outer ear infections (which is the main reason I wear earplugs for swimming) you'll want to replace them more often.