Quite apart from the issue of any dog being alone for some hours during the day, you need to think about potential relationship between a dog and your son.
If it was an older dog, they probably wouldn't be so interested in playing very much with an 11 y/o (not to the same extent as a younger dog anyway). They would probably be sleeping more, could be slightly grumpy if your son came and wanted to play when they wanted to sleep etc.
You also have to be realistic that you would need to do a short walk in the evenings with the dog, perhaps having to leave your son in the house while you went round the block for 20 mins in the dark (winter time). When you want to have days out/hols/half term with your son, you would still need to pay a dog walker if you were planning a full day out, to pay for kennels if longer holidays happen where you can't take a dog etc etc.
Do you have "spare" money to pay pet insurance every month, vaccinations every year, worming and flea treatments regularly plus dog walker every day - just the dog walker would be around £10 a day. Any visit to the vet could cost around £50-70 easily, you wouldn't claim it back on the insurance 'cos the excess payment would probably be about the same. Food roughly a £1 a day plus extra toys/treats you'd probably want to get.
It does add up - if you're the sole wage earner, you really have to think about whether you want to use that money for a dog or whether you would prefer to use it to buy things for you and your son, enjoy days out, trips to the cinema. Dogs are fantastic but they are not cheap nowadays and they are a serious commitment in terms of time as well.
Apologies for length!