Wiggle, poor you, that sounds rough. Just remember, there's no easy answer as to whether to go ahead, so don't beat yourself up about 'making the right choice'. The choice itself isn't the key, it's your attitude to the choice once you've made it. Hope that doesn't sound preachy.
We were lucky with schools as we are in Scotland, and most people simply go to their own catchment school here, and you're supposed to be guaranteed a place (it doesn't always work out, but usually does). Some people ask for placing requests but it's not the norm. My DS is now in Primary 3, so I've got used to him going off every day and having the day to myself - it has allowed me to explore quite a few things. I work part-time, I did an OU course, I joined the gym - usual stuff really, and although I did miss him at first, it is nice to get a bit of my old identity back (I think most SAHM mums would agree with me on this).
As for DS being an only and getting spoiled, I don't know whether he is or not. I probably don't stress as much as some about how I'm going to pay for things like swimming lessons or new shoes, but re toys and so on, I think he's probably somewhere in the middle. I think your own family values tend to kick in in this respect. I was more worried about making sure life didn't become 'all about DS' but to others it probably seems as if it is. I mean, when you share stories with other mums you're going to talk about your only and no-one else, aren't you?
Our somewhat flawed solution to take the heat off DS a bit was to get a dog - the dog has done a lot of things a sibling would. He's stolen and chewed precious toys, his needs have to come before DS's sometimes, like if he needs a walk, and he gets quite a lot of attention. On the plus, he's good company for DS, who like to snuggle with him in bed (dog loves this, as he isn't allowed on anyone else's bed - hope no-one from the pet thread is reading, as I may get told off!), and DS thinks of him as his best friend.
Anyway, I've done it again - written a huge long post and hogged all the attention. I really need to learn how to be more succinct. LOL