Thanks for all the comments. In the end I bought a second hand Steam Deck 256GB on ebay. It's a fantastic bit of kit and as others have said, literally a game changer. Not being tied to the TV opens up more gaming time for me.

I've also bought a memory card and so far I've been playing the following which run great on the deck (after researching the optimal graphics settings online):

Forza Horizon 5
GTA 5
Cyberpunk 2077
No Mans Sky