A few comments:
A 27sqft house is pretty small. How do you get two floors in there?
Look for no cost solutions.
Try your speedtest at different times of day and with other people on the net
Can you move your router to a more central location? For a 2700sqft house you shouldn't need a mesh system or any additional hardware
That said, do you have cable outlets upstairs where you are running into the problem? If so, you can set up a MoCA system
Ethernet Over Coax?! A Complete Guide to MoCA Adapters - TechReviewer that works great. Unless your internet provider is set up for MoCA then you'll need one box on either end. The boxes are about $50 each and I have a spare if you want for the postage.
I have one of these running in Santa Fe and have extended the network from the main house to the Casita (a second house about 600ft away) with one coax cable. You can either use the two little boxes (that just give you an ethernet port at the remote location (and the cable pass-through) or a little box on the router end and the bigger wireless router on the other end that adds wireless.
Because it is hardwired, the speeds are consistent and aren't affected by somebody heating a cup of coffee in the microwave.