Welcome to the great sport of springer air rifle shooting.
The size of scope you use also depends on light levels so for general plinking either at home or on a club range you should go for something like a 3-9 x 40. The mounts can be either the single mount or twin mount types but whichever you decide on they should be just high enough for your scope to clear the rifle body. You should also use a 'scope arrester' to prevent the scope from creeping during recoil.
Your best bet would be to visit a local club range with a shop and have a chat to them cos most have used items for sale.
Good luck in your venture and shoot safely.