The cheapest method, in the long run, would be to buy a console with an optical drive. You can buy the games from Amazon etc, or even here on the members market, for considerably less than what is available on the Playstation digital store. Of course, if you'd prefer not to have any physical media cluttering up the house then you could go all digital ; but be warned, prices are higher within the "walled garden" of the Sony marketplace.
If you've never played any Sony games before, the PS Plus/Extra subscription represents good value for money. It basically has almost everything that's on Xbox's Game Pass, minus a few Xbox 1st party titles. The only snag to be aware of is that Sony's own 1st party titles rotate on/off the platform - they are not persistently there, unlike on Game Pass.
How well Portal works will be completely dependent on your wifi / broadband connectivity. If you have a decent service then you'll be ok ( within your house, at least ). Portal can now do cloud streaming, which means technically you don't need to own a console ... just have a PS account plus subscription to access games. According to Digital Foundry, the performance and latency is similar to streaming from a local console. Of course, this assumes your wifi service is adequate.
Btw, have you considered a Steam Deck ? You'd have access to almost every game ( via Steam ) including many of the Sony 1st party titles. If I was going to have limited/no access to TV gaming then that would probably be my choice.