I agree with both those who say put effort not developing your friendship network and those who say get a pet. I was married for about a hundred years, but was never ever looked after. When I was in hospital I had to get a friend to come and collect me as he couldn't be arsed to visit. So having a bloke is not necessarily the answer.
I only have my mum left and she has profound dementia so no support there. Rather the opposite in fact.
However, my female friends have been a long running source of support. I don't have masses, but those I do are utterly supportive (in different ways, its a bit horses for courses). I also have pets. In the evenings when the kids have gone to bed, I love a cuddle with a dog or cat, or both. They are always pleased to see you, welcome you home, always want a cuddle, give unconditional love and never ever criticise. A huge improvement on men!
More seriously, on days when you just can't face getting out and about, if you have pets you have to get up and if you have dogs you have to walk them. I always feel better for getting out and even just saying hello to other dog walkers is a mood lifter.