TennisTV would be a good subscription to get.
Has most matches from most tournaments. It has a 'DVR' mode so you can rewind etc. (So you could open the streaming page as a match starts, save the link, and then reopen it when you have the free time to watch. I did this quite a lot while I still had TTV.)
They also save 'matches on demand' including the finals of all 500 tournaments upwards (I think).
Btw, many matches are at night, and semis and finals are almost always at the weekend, so it's not as bad as you think!
Thank you everyone for your posts. And sorry I didn't notice earlier that this thread had re-opened.
I guess most people will just watch odd matches on nights when they can? And keep up other times via interactive scoreboards, news articles etc. And then watch the finals when they are on on weekends.
Don't get me wrong, I love this sport. And I don't want to keep up just "for the heck of it", it gets me excited and I want that excitement to continue throughout the year, not just when I'm off work... I just don't really know any other tennis fans personally and I do see others around me struggling to try to balance the love of this sport with a full-time job. And it annoys me that it seems so easy for fans of other sports whose matches aren't always scheduled mid-week!