Hi Danielle,
One way to help increase your supply is to pump after more feedings. I know it's a lot of work but your body works on supply and demand. The more you drain your breasts the more milk your body thinks it needs to produce. Do what you can, I know it's a lot of work.
As for the scale, you need something that can measure in ounces. Most baby scales are curves so the baby doesn't roll out. If you don't want to purchase one, you pediatrician may let you come to the office and weigh before and after a feed.
Your body may very well keep up with your baby's demands. It varies person by person. If you find that you aren't keeping up just know that babies go through growth spurts and it may take your body a little time to catch up. There is more to breastfeeding than the milk and I know it's easier said than done but don't beat yourself up if you have to supplement. You are doing everything you can.