If you don't want Net Speed in the systray and are open to considering another option, might I suggest conky
? It's a light weight system monitor that is highly configurable and immensely popular. You can almost say it has a cult following:

Near the bottom is a real time display of network speed including graphs. Also vnstat
is used to list total network traffic for today, yesterday, this week and this month. You can set the month to your ISP's billing cycle, ie April 16 to May 16.
To install conky use:
sudo apt install conky
To find a plethora of custom setups for conky
see Ubuntu Forums.