There are a few breathable sleep surfaces to choose from that will lower the risk of SIDS and suffocation when baby sleeps on belly, and also leave baby less sweaty. On a regular surface, the concern is that carbon dioxide gets trapped and rebreathed by baby. A breathable surface allows the carbon dioxide to flow freely away and provides baby a fresher breathing space.
Discuss with your pediatrician how many ounces the baby should be getting per 24 hours, and how many ounces in how many total feedings. If for some reason baby isn't getting enough, discuss with your doc and LC a game plan. It may be an issue of tongue tie or incorrect latch, or needing to increase supply through diet, hydration, and pumping.
Traditional digital baby scales run around $50 and are good through about 60 pounds. And interesting (pricier) option is the Hatch Baby Smart Pad - a "smart" changing table and scale in one that connect to your phone via wifi and keeps track of weight, feedings, and diaper changes! ($249 on Amazon)