I had a similar issue. Powerline adapters were looking like a great option specifically because I had just moved into this house and was absolutely clueless about the existing cabling in walls (some of which turned out faulty), and networking in general.
Your ideal situation would be to hire a contractor to run networking cables through floors and walls. This could be pricey.
Similarly, my router was in the basement at one extreme end and I had almost zero connectivity on the first floor - it was affecting the marriage. For short-term relief I bought a range extender with an Ethernet port and was able to wire at least one device and improve WiFi signals - this saved the marriage.
When I had the time and the courage, I was able to replace the faulty wiring and relocate the DSL router between the basement ceiling and the ground floor, floor. Then, from the router I pulled an Ethernet cable into a 8 port Gigabit switch which now supplies to my PC, Smart TV and receiver. Turns out the previous tenants had laid out some Cat5e cables rather strategically which simplified matters for me. Now my desktop and entertainment devices are wired in the basement.
I am not using the WiFi Extender and can average 12Mbps on the 2.4Ghz and 25Mbps on the 5Ghz band on the first floor's extreme ends after optimizing the channels. This is a huge improvement. Though, my townhouse is half of yours.
My next task is to utilize an old 2.4Ghz router to create an access point feeding from the switch which I hope will further improve first floor penetration.
I shared my story because I would definitely recommend BuddhaSkoota's solution to strategically place a couple of access points. Wired is the way to go - at least in part.
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EDIT:
Is the forum acting up? Failed to process reply on multiple accounts. Luckily I had copied the text.