Day trip to cotswolds

Go Cotswolds is a really convenient option if you are ok with a small group tour. You can take an early train from Paddington to Moreton-in-Marsh and they will pick you up at the station:
https://www.gocotswolds.co.uk/

I took this tour pre-pandemic and it was a great way to see a number of the villages in a single day. We also had time in several towns to explore on our own and a break for lunch.

A nice and easy day trip, which we have done, is take the train from Paddington to Moreton-in-Marsh, then get a bus to Bourton-on-the-Water. It's a very cute town and from there there is a very nice walk via the Slaughters into Stow-on-the-Wold which is another very cute town. From Stow-on-the-Wold you can get another bus back to Moreton-in-Marsh and train back to London. Good luck with your planning!

Link to an example walk: https://explorethecotswolds.com/stow-on-the-wold-to-bourton-on-the-water-walk-cotswolds/
It's just over 4 miles.

I took the train from Paddington to Morton And Went with GoCotswolds.com. they had quite a few options and I had specific towns that I wanted to see so I suggest you look on the website and see what they have to offer that you might like. Correspondence with them was quick, easy and kind. Guide was terrific. The Cotswolds was one of my goals on a 5 week trip to europe. Going with gocotswolds.com made it everything I wanted to be and more!