Hi - We found what we think is a great mattress @ USA Baby, but it's a bit pricey and we are not certain if the features are truly good or just gimmicks. 1.) It is very firm foam on one side and coil on the other. The idea is to be able to flip the mattress and use it as baby gets older. 2.) It also touts squared corners -- which the sales associate says is much better than rounded corners. However, we see no other mattresses with squared corners... 3.) And the mattress can come upgraded with a vibrator. What is your input on all of these features? The mattress is fairly new so there is no info in the bargains book. Thank you!