It's like anything really, you get what you pay for.
That said, if you've not had a new tv for over 10 years then you'll definitely notice the difference for the better as, yes, technology has moved on.
I would suggest a 50'' and i would also suggest using either Richer Sounds or John Lewis as RS gives a 6 year warranty and JL gives a 5 year warranty.
I have an LG OLED which is five years old and it's been great and it's interface and remote are very user friendly and simple to use.
I would spend a little extra for the better quality tv, i would look at the LG 50QNED816RE @699 - LG OLED48A26LA @799 or the Samsung QE50Q80C @799
The picture quality on the LG OLED is superb, but i'm slightly biased to LG as i own one.
I'm in the market myself for an 85'' inch and i keep being drawn to another LG as i've been happy with what i've had.
But, you'll get similar response's from Sony, Samsung, Panasonic owners.
Ultimately it's your choice as it's your money, but as i've mentioned, spend a little extra for the better quality tv and you won't regret it.
Hope that helps and good luck with what ever you end up buying