I don't think you are selfish, quite the opposite. I can completely understand the want for a fourth, as I sit here pregnant with number four. I believe people are born for a reason, and nobody is an accident, and so this isn't buying a new handbag when you already have three. It's like you are looking around the dinner table and your heart feels there is someone missing, someone who should be there.
I have a friend in America who has had 7 c-sections and she is currently pregnant again. Her ob is obviously monitering her closely, but sees no reason why she can't have as many children as she wants, baring unforseen circumstances. It sounds like you'd be an excellent candidate for another as you have had such smooth deliveries.
I would personally say take this year to heal, and just enjoy your wonderful little girls and then make a decision then, your dh will probably be more keen when he isn't currently holding a newborn, and then if your heart is still longing for that missing person, I would say go for it. But I'd happily have a few more so maybe I'm not the best one to ask.
xx
