I am an only child and I love it! My mum tells me there were times when I asked for a brother or sister but I can't remember it. I had my mums complete attention all the time and we had a good relationship growing up. I was lucky to have lots of cousins and close friends who lived next door so I always had kids to play with. I now also have 2 SIL that I adore.

We considered ony having 1 but eventually decided to give #2 a go. They do love each other and I watch them and the special relationship they have and often question my DH if it was like that with his 2 sisters and tell him how lucky he was. So yes there are benefits but my son sometimes feel we don't give him enough attention, my daughter feels my son gets more stuff then she does and I feel torn in two 80% of the time constantly trying to 'be present' for both in equal measure with their unique interesdts and takes on life. So it has it's draw backs as well.

The most important thing is
1. as a child growing up I never felt like I was missing out
2. as an adult looking back I certainly don't feel resentful for not having a sibling.

Hope you can find peace with whichever road you take