We bought a treadmill a couple of years ago and ended up with a NordicTrak (
https://www.nordictrack.co.uk/) and iFit subscription. Since we have had the treadmill other parties like Peloton have jumped into the game.
Our model is discontinued - however as we went for a reasonable spec one we do not feel hard done by as the majority of the benefit comes from the interactive programs.
We have the iFit subscription (part of Nordictracks service and renewable each year) and although it is quite americanised we have found it good and the content has been getting better and better as the years have gone on. Sandra is usually on the treadmill 2-3 times per week and usually does either a live or pre-loaded session.
Couple of things I would recommend you try to get:
- Decide whether its for running or walking (determines the incline)
- Biggest screen you can
- Get someone to fit it - saves a lot of hassle on any warranty claims (albeit we have never had to use it)
- Have it located downstairs (they can make a lot of noise) and fit a sound absorbing mat on the bottom
- Heart rate monitor is a good edition
Happy to have a look at ours if you want to get an idea of the iFit program

Also Powerhouse fitness on Leith Walk is a good place to go for advice.
Any questions then feel free to ask
Cheers
George