sudo apt install gnome-shell-extension-system-monitor
Once you've got it installed, reboot, then open the Tweaks application and enable System-monitor.
You can set it so the CPU, GPU, Thermal, Drive, Memory, etc. show up in the taskbar, or in a pop-up from the taskbar.
And you can set it to display as a graph or as digits, or as both.
There is one glitch... if you set it to show all the cores of the CPU individually, you can't take it back... it'll continue to show all the cores even after you deselect that option. So do NOT click "Display Individual Cores".
But otherwise it's a pretty slick little app.