I had my beautiful boy when I was 40. I was never toobothered about having children but we fell pregnant by surprise and as soon as i had my wee boy i knew i wanted another. I am 43 next month and today I have woken up to the fact that its just not going to happen. We are not in a position to try any of the artifical method of conception and i think im too old, broke and fat for it to have any chance of success. I really wanted another baby, i was cluless the first time round and think i would do such a better job this time. My DS is so wonderful that i think he would make such a lovely big brother. My husband would also love another baby. We were byourselves for so long and this little boy has turned our lives upside down and we love it! Having another one would be fantasic. We have been so lucky and fortunate that we have no right to ask for anymore but I still keep wishing, keep hoping that maybe........ This might sound really stupid but im also worried that when his dad and I are dead that he wont have anyone truly in his corner. Who will keep an eye out for him, make sure he's safe?
I know you said you don't want to try any of the artificial options, but have you considered seeing a doctor to discuss your choices anyway? There may be options other than ivf which are less intrusive (I'm thinking Clomid as its the first thing that jumps to mind, I'm sure there are other treatments that may help).
I was a similar age to you when I had my child. I hope (and am trying to install the social skills to support this) that by the time I shuffle off this mortal coil they'll have a partner and/or circle of staunch friends who will be truly in their corner, which is how it is for me.
Sibling relationships can be life-affirming but quite often they are not. Make a decision about assisted conception that works for your family but don't base it on a romanticised idea of what sibling relationships are like.