i live in Arizona, it is really hot here. It is definatelty ok to just wear a onesie. They make very cute ones.
go buy a onesie and stencil it on the onesie urself. It'll be just like u want it and cheaper in the long run for u. You can bring a onesie to a t-shirt print shop and they can do it for u too. They may be able to even embroidered it on it for u.
They're really fun. I went to a 2 year old girl's birthday. Gymboree has play equipment for kids from 6 months to 5 years. If all the kids at the party will be around the age of 1, then the Gymboree folks will arrange it for that age. At our local gy...