So buy changing ISP's you may be able to save a few dollars a month or maybe get some goodies chucked in for a couple of months (Neon,Amazon maybe), but only if you sign up for a fixed period. You will run that usual risk of getting your change screwed up and having no internet for a period of time.
Sure - many have a smooth switch, but there are plenty of threads on this site about changeovers being stuffed up resulting in no internet for a while - just worth mentioning.
Looking at your original issue, I am quite confused if the speedtest you supplied is on wifi or wired.
If its wifi - then ok - that's wifi with walls/ceilings for you.
Does a speedtest at the router with a cable show 300/100? If so then you are getting what you pay for - if not - something is very wrong.
Looking at the logistics of your 2 storied premises, have you considered a wifi mesh system?
I have been mulling that same sort of issue and physical layout at my place
Maybe this:
https://www.pbtech.co.nz/product/NETTPL9402/TP-Link-Deco-M4-Whole-Home-Mesh-Wi-Fi-System---2-P
If you scoot down to the section "Wi-Fi Dead-Zone Killer" that multi story home scenario probably fits.
One of the units would be connected to the UFB ONT (the downstairs unit in my case (and yours)) and the other (upstairs) connects using wifi to the main unit. So they work as one wireless zone.
PS Getting the ONT moved is $$$$$$$$$$. Search on this forum and see what people have been quoted.
These units also have an ethernet port if you needed to connect something with a cable.
Or you can buy a pack of three if you want to chuck another router/wifi repeater into the mix.
https://www.pbtech.co.nz/product/NETTPL9403/TP-Link-Deco-M4-Whole-Home-Mesh-Wi-Fi-System---3-P
