Talk to your landlord and tell him you’d like to install a network socket so that the whole house gets better WiFi, and that you’ll leave it behind when you move so it won’t leave any mess and will benefit future tenants too. Most landlords I’ve tried this with have jumped at the chance.
Failing that, dropouts suggest interference rather than just signal problems. Try running a channel monitor on your phone and see if there’s anything using the same channels as your WiFi, try switching to another channel and look for anything happening that coincides with the drop-outs (microwave, certain lights, electric motors running, etc).
Lastly a better modem might just do the trick. I’ve found that anything running OpenWRT is ten times more reliable than most other options, particularly when placed under heavy load or difficult circumstances.
Power line adaptors aren’t bad, but they are hit or miss. If they hit, they’ll work well and solve all your problems for minimal cost and effort. If they miss you’ll probably never get them working properly. It’s a bit of a gamble, but I wouldn’t rule them out.
Wireless range extenders/access points/mesh networks are the reverse. They’ll almost always work, but they make the inherent problems with WiFi worse. More latency, more congestion, more interference. They’re not without downsides.
Running a cable so you can move your router to a better location would be my number 1 choice. Ideally somewhere where you can plug multiple devices (TV, consoles, pc, etc) into it so they aren’t competing with the devices that really need the WiFi.