Don't give in to the hype dissing only children.
Hi, I'm an only child and my mother was also an only child, so yes, holidays were pretty intimate affairs at our home (especially since all my dad's relatives were out of state). I grew up pretty pampered and adored by my parents and grandparents, I won't say I wasn't spoiled. However, when there's no siblings to share chores or blame or boredom, that tends to level out the spoiling and give you a more sensible perspective of the world.
When I was very young I liked the idea of having siblings, but when my mom decided not to have another, I wasn't that bummed. In all honesty, I would have appreciated a puppy just as much. I had friends that I considered my siblings. I experienced the "joy" of younger and elder siblings through my friends siblings. I realized they weren't all that great to have around. They weren't cute playthings and, ultimately, they drove you nuts.
I think I came out pretty well adjusted, regardless. I went to a good university, a good professional school, married a good man, got a job that pays my bills, and was never a burden on my parents after undergrad. I have a good relationship with my parents and my one remaining grandparent.
I see others have posted about dealing with an aging parent as an only, and I know my mom has had to go through this with her parents. It's hard of course, but it's not like she's alone. She has me! She has my dad. She has her friends. Geez, having siblings doesn't guarantee they'll offer any help with aging parents. My dad has 3 sisters and lived out of state from his ailing mother. He didn't care for her in her later years, but neither did two of his sisters who lived a lot closer. Conversely, he was the one who took care of their dad (who was in state for us), without much sisterly help.
I very much want a girl. If I have a boy first, I'll try again. But if I had a girl the first time, I'd probably stop right there. Only girls have worked well for our family thus far, I see no reason to buck the system now.