I just want to mention that polyurethane is a pretty dangerous, awful material. I would avoid it for your mattress. Polyethelyene is a much more inert and save material. I would have bought an organic mattress but they cost an arm and a leg. Instead, I found a used Sealy mattress with a vinyl cover. Used is ok if it is in good condition and most of the bad toxins will have already been released into the air (most plastics "off-gas" chemicals that are not always safe).
I bought a solid wood convertible crib with a high back from JC Penny. It does look very nice but sometimes I wonder if I should have gone for a more basic model since the crib is only used for a couple years. I think it is going to be a royal pain to lower the mattress--that is something for you to consider. On the other hand, the crib will grow with my daughter. We have been happy with it thus far. We did not use bumpers--too much of a pain to put in and take out and dangerous too. I suspect that all mattresses are a pain when it comes to changing sheets!
You may also want to think about storage needs. Some models come with a drawer underneath the crib. Might be useful if space is lacking. Make sure that the joints on the drawer and other crib parts are well designed and will hold up to wear and tear. Good luck!