@Sky Aisling :-
Hallo, Sky.
I know exactly what you need. A few years back, I was in the position of having a fairly low monthly data cap on our IP's broadband plan, and needed a way to keep an eye on exactly what I was using. Their penalties for going over the set amount were a bit on the steep side!
So; back in 2014, I did some scouting around to see what I could find. I found a brilliant wee app, coded by a guy name of Rob Dawson, here in the UK, which did exactly what I wanted. It's called
BitMeterOS
.....and you can find the forum thread I started to 'share' it a year later, over at the old forum:-
http://oldforum.puppylinux.com/puppy/vi ... a143bf9f5d
It's a small .deb package, which displays via a tab in your browser; quite fitting, considering that the browser is the source of most of your data consumption anyway. If you go to Rob's CodeBox website, there's even an interactive 'demo', so you can "try before you buy", as it were!
http://codebox.org.uk/pages/bitmeteros
(It's completely free, of course.)
Go to the above CodeBox link, and click on the 'Demo' link on the left-hand side. What you will see (using 'dummy' data generated by Rob's server) is exactly what you will see in a browser tab when you have it installed.
----------------------------------------
If you decide to give it a go, take my advice; go for the older, 0.7.6 version. This only measures a single OS's usage at a time, but it is 100% rock-solid stable. The newer 0.8.0, by means of using clever network commands & stuff, is supposed to be able to concatenate totals from multiple OSs.....but Rob was experimenting with a new type of database when he wrote this, it wasn't very stable, and it crashes. A LOT. And he never bothered to re-write it, as he'd moved on to newer projects.
Makes far more sense to stick with the stable version that works!
----------------------------------------
Once installed, you bring up BitMeter's web-interface by entering the following URL:-
http://localhost:2605/index.html
(Note; this is good old-fashioned "http", NOT "https". It's not needed for a purely 'local', internal connection.) Once the URL is 'up', it makes sense to bookmark it, so you can call it up whenever you want. I have all my browsers set to open up with two tabs displaying; BitMeterOS in one.....the Puppy Forum in the other.
This will give you access to all BitMeter's functions. For your purpose, the 'Summary' tab is probably the most relevant one.
I don't really need this anymore; we switched IPs a few years back, and now have an unlimited connection.....but I keep it around, 'cos it only occupies a few hundred Kb, and is still remarkably useful. Hope that helps!
Mike.