I get the itch to try to give M a sibling just about every few days. We can't comfortably afford it right now...maybe once he is getting ready for kindergarden, but not right now. Everyone says "You'll make it work." And I know they're right, but we'd rather not have to "make it work"...we'd rather it work easily. It will avoid lots of arguments. :-)
I'm also torn about whether I really want to have another baby or if I just want M to not be alone after we're gone. I know lots of only children who are well-adjusted-thanks to their parents for making them that way. So some days I feel like I really just want to give ALL of my love to M and have plenty of extra cash to help him succeed. I just love him so much I can't imagine sharing my time/attention with anyone else.
I also spent the weekend with my superhero cousin who has a 2.5 year old and a 2 month old. She was exhausted. She didn't have time to focus like she wanted to. Her son, despite all her efforts, felt abandoned sometimes (not last weekend, but other times). I just don't know how I could deal with M ever feeling abandoned...even knowing it's for his baby sister/brother and that he'd understand one day.
So we'll probably revisit the idea in 4 years and see how we feel then. :-) It's a tough, tough decision though!