May as well go for whatever plummeted price 4k TV you feel comfortable with but if just a casual TV user and not a movie buff etc then don't get tied up with the 4k bit as there is next to no real 4k source material. If you really want to go that route you'll be chasing down a 4k uhd hdr set a bluray player that outputs in the same hdr, or an online source that you'll pay a subscription to sky/netflix/amazon etc, as for the sound side of things a soundbar is better than the TV sound but not a patch on a proper full thx or dolby atmos setup.
I would advise you to grab a few home AV magazines to get a handle on the jargon and lingo and let you have an idea about the size of the rabbit hole you could fall down if swayed by a sales person.
I myself am currently modernising my audio side of things, it can be a very expensive hobby and am considering one of the Oppo bluray decks over the commonly available Sony or Panasonic players to go with my latest Onkyo AVamp, as for the TV side of this gs I am considering a projector over the current TV.
As bilbo bagging said it can be a dangerous business stepping out of your door.
