Though I've not tried it, I imagine Wingspan probably has a decent solo game - Stonemaier seem to spend a good amount of resources on their Automa system (basically a pack of cards that simulate another player). There are also some good dedicated solo games that I've heard of; Mr Cabbagehead's Garden & Coffee Roaster are two I've heard good things recently about.
Ones I have played myself and enjoyed are Terraforming Mars and Glass Road. I believe most Uwe Rosenberg games have a 1 player variant, but unless you enjoy the base game (as I do with Glass Road) and enjoy a high-score challenge, they usually feel like something is missing (i.e. other players!).
I do play online games regularly too - especially on Yucata.de as it hosts several games I really enjoy and can play in near-realtime (other sites like BoardGameArena are real time), and still get to play against real people rather than a deck of cards or an AI.
I would echo some of the other folk on here - it can be hard to meet new people, but as SimonC says above (I go to the same club), if other clubs are like ours, an evening gaming there is super welcoming - we've had several people come along for the first time and we've welcomed them, and not put any "social pressure" on them - we're all there to enjoy a game first and foremost.
Also, there are some good places to find more about single player games, e.g. SoloMode Games on youtube.