Ok, so your TV would have it's bottom at a similar to height as the one in our kitchen shots. That's not too high with your sofa seat (46cm vs our 30ish cm). Plus you'll be slouching down with a blanket in your drunken state so you will be looking up a bit anyway
As you're sitting 3.5m away I'd say a 55" would be ok, but to see the benefit of HDR etc and really get the big screen effect, a 65" would be ideal. TVs these days have much thinner bezels than that ancient one in the corner, so blend in better.
For TVs:
- Grab an angled bracket like the Invision one. It doesn't stick out much and you can angle it downwards a little.
- I'd look at the 2019 Samsung models - Q70, Q80, Q85 (ignore the Q60 unless it's a super cheap deal).
- Or consider an LG OLED, but they will probably cost more and you have the risk of screen burn to have in your mind. Lovely picture though.
- Both have decent SMART systems with almost every app you could need. I liked the LG but am very impressed with the Samsung system since we got our Q90. Just brilliant and easy to use.
For Sound:
- Depends how much effort you want to go to, be it a 5.1 system or go for a Soundbar with Sub system (maybe add their rear speaker set).
- A full system with AVR will be better, but you'll have to mount speakers on the walls, chase/hide wires for the front 3, run wires to rear speakers and sub etc.
- A soundbar setup will let the soundbar do the front 3 channels and will give some height (if it has upfiring drivers), look at the Samsung Q60r or Q70r 2.1 combos as they come with a wee sub.
- You can then add their SWA8500 (or SWA9000, which is meant for your chosen soundbar) wireless rear speaker kit if you really want rears.. You can hide the rear wireless box at the back of the room then only run cables to the rear surrounds.
If I was in your position and wanted the least hassle for the best buck, I'd get one of the 65" Samsung 2019 models (Q70 minimum, or the Q85 as it has reflective coating), then something like their Q60r or Q70r soundbar 2.1 kit. You'll then get the big screen for general viewing and perfect for evening movies, no risk of screen burn (like the LG OLEDs) and you'll get decent enough sound from the soundbar/sub combo and have very little cable management to worry about.
It's easy on here to spout, get an OLED, get a 7.1.4 surround system, but you can get an incredible picture from the Samsung QLED sets and decent sound from their soundbar combo. It won't be a full surround setup, but then it'll be a lot less hassle, easy to use for both you and the GF/Mrs and it'll be easy to install in comparison. A decent compromise.