Our first son BEGGED us for a sibling. I never even wanted ANY children. I liked my life, so when I found out I was pregnant with him, I freaked and cried. I got over it and nurtured my body and baby. So, after a homebirth and a long delivery, I really had NO desire for more kids....but our son begged us and we realized how important that might be when we die. Being left alone on this planet seemed unfair, as I watched an older woman, with no children, a dead husband, no siblings and no parents dive into demetia very quickly. (Not that demetia is caused by having no one around, but she really had NO ONE and that made me really sad.)
We decided to try for #2 when our son was 3. It took us 3 months of trying to get pregnant and some progesterone cream. He was 4.5 WEEKS late, over 10 pounds and a really intense homebirth. I WAS DONE. I even had an appointment made for my husband with a local urologist for a vasectomy appointment. He decided he was about 85% sure he was done having kids. REALLY???
I should say that I own a local business that my husband now runs with me, but at the time, it was me working and bringing the baby to the office to breastfeed all day long. My husband was home watching #1.
A little over a year later, I became pregnant with #3, who is 22 months younger than #2. What on earth were we thinking? Another homebirth and a really dramatic girl showed up. I was SOOOO done. My husband refused to get a vasectomy. He's not sure he's done. REALLY?
About a year ago, when #3 was 2 years old, I started to feel "not done" having kids. (I'm pretty sure I'm nuts. LOL) I am currently a week past my EDD with #4 - but I can tell you, I AM DONE....without a doubt and so is the husband. We have great kids, work and homeschool. His vasectomy appointment will be made after this baby shows up, by HIM.
My point is, I went from wanting NO children and having some great vacations to having almost 4 children and giving in on how I spend and save my money. I can tell you, siblings are great for our kids. Even now, they are so excited to meet the baby. When I told my oldest we were pregnant, he hugged me so tight and said, "Thanks mom," like I was giving HIM a present.
Having a sibling allows you to bounce ideas off of them and feel connected in a non-so human connected world. The idea of your life changing like that IS scary. I'm even freaking now about how we are going to find our balance again, but we always do. Having one kid doesn't mean that life will always be perfectly balanced and calm, but having two means they have someone to lean on when life is not balanced and calm - and you and your husband are not alive anymore to protect your son. Very rarely do we think past our current lives. There are no certainties, so just breathe and follow your intuition.
Good luck.