Mavis, just saw this - I'm in much the same position as you but for longer - DH died nearly four years ago, and have DS 11 and DD 7. I also can't see myself starting any kind of new relationship for the foreseeable future.
I had the same concerns about DS, and so far what I have been doing is making sure he spends time with his uncles - unfortunately none live close by, but we do spend Christmas and go on summer holiday with one for a couple of weeks each year. He's done things like take DS to rugby/football games with his older cousin, and also subjects DS to the kind of blokey teasing and banter that he doesn't get at home. He's getting better at dealing with it....
Also, he has a sort-of godfather - I'm not religious, but this is a family friend who agreed when DS was born (and DH was still alive, obviously) to be a non-religious godparent for him. He's been living abroad for a while so we have only seen him once or twice a year, but he's moving back to this country soon, so I hope DS will see more of him. He is taking the responsibility quite seriously, and by a sad coincidence he also lost his father at a similar age to DS, so can be a good role model/sounding board.
Do you have any good male friends or relatives who might be willing to take on the role of special uncle/godfather as your DS gets older? Doesn't have to be an actual uncle - sounds like the ones you have are not ideal - but do you have any cousins or good friends of yours or DPs who might step up to the mark?
Also, although I am not a particular fan of single-sex education, I chose an all-boys school for DS when he started secondary this year (it was the school he liked best too, luckily), as I think the blokeish atmosphere there is a good antidote to his rather female-dominated family and home life. Though I do try to do some fun stuff as well as all the usual single-mum responsible stuff, like take DS on a high-ropes and zipwire course, or launch the occasional tickle-attack .