foxyfemke
sorry to hear about your mum. Sounds like you're in a similar position re: another child. The more I think about it, the more I think not risking another pregnancy is the sensible thing to do.
FiveShelties thank you for your two sided balanced view!
Summerorjustmaybe I'm actually enjoying being dog-free currently! We recently lost my childhood dog (he came with me when I left home) at almost 20 years old and as much as I loved him and it broke my heart when he died, I'm quite enjoying not being quite so tied down! There will definitely be another dog on the cards in the future.
EggAndButter thank you. I guess one good thing is that my son will be part of a big family even if there aren't any siblings. There's not much on my side for one reason or another but my husband's side are a big close knit bunch and I have a number of very good friends that form the basis of my "family"
Prudho I hope all is ok 
BogglesGoggles you've made me realise that I'm effectively in a similar "only child with elderly parent" scenario, although in my case it's an elderly uncle. He never married or had children, his parents and brother (my dad) are all dead, it's literally just me and him on that side. I'm listed as next of kin, have power of attorney over medical and financial dealings etc. and he does have physical health issues which regularly see him in hospital (on average about 4 weeks at a time two or 3 times a year). I know in the future I'll have to make decisions regarding his health and care and stuff but actually I'm ok with that.
horizontalis I'd say I'm similar regarding liking my own space and company! Whilst my mum is still alive, our relationship has been difficult (and now NC, my decision), I pretty much had to fend for myself from the day I left for uni. I had no emotional, practical or financial support from her at all but my determination and resilience got me through. I guess those are good qualities to instill in my son for the future!
RavenLG we can provide chaos! Interestingly holidays are one thing I've considered quite a bit. I never had holidays as a kid, but I can't imagine traipsing around with just your parents as a kid is much fun. We'd be quite willing to take a cousin/friend with us once he's old enough to want peer company. We also all go on a big family camping trip each year (with all cousins he's up to 7 now!) and birthdays are generally a big family day out somewhere.
DreamingofSunshine I'm in a similar boat with my siblings but my husband and his family are so close, I guess it's opened my eyes to what our son could be missing out on
Thank you to everyone who has taken the time to comment, it's been very useful!