Warning: product endorsement ahead.
Something that I like to do as a way of keeping an eye on things is to periodically take my measurements. I do this quarterly, it is long enough to show significant progress between measurings. It can also be really encouraging when it seems that progress seems slow. (and helps when shopping for replacement clothing)
I have always just used a cloth measuring tape meant for sewing. I ended up getting this specific body measuring tape as sort of an accident, it ended up being free when I had it shipped with something else.
The Myotape
Getting the measurement right if you don't have someone to help is kind of tricky. I would keep dropping it, or pulling it too tight, or leaving it too loose.This little thing makes it really simple. You just put it really loose around the body part and put the little pin on the end in the holder, then you just push a button and it automatically adjusts to the proper tension and holds it there. Then you can just unhook it and easily get the correct reading. You get the same tension every time. It seems like a little thing, and I never would've bothered with it, but I find it is a really cool little device.
It's $5 on Amazon.