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.