One of the newer items for the nursery is the round crib. The mattress for this crib is a 42" round circle. This has both advantages as well as disadvantages. Round cribs are unique and make a bold statement in the nursery. Being a bit smaller, it takes up less room, and being round, it can easily fit into the middle of the room allowing for more use of wall space. You can also find more information about different matters at https://caricotemp.com/.
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They also do not have any sharp corners to run into in the middle of the night. Depending on the particular crib, it can allow more unfettered access to the child from anywhere in the room.
On the downside, round cribs are a bit more expensive than standard cribs, the mattresses are harder to come by and there are not nearly as many options when buying bedding as with standard sized cribs. Also, a round crib mattress is only 42" from edge to edge. A standard crib mattress is 52" x 28". So you can keep the baby in the crib longer with a standard crib mattress.
While that might not seem like a viable option, there are many beds that allow a toddler to transition from the crib to a bed. This bed is much lower to the ground than a regular twin bed and has guards on the sides so your toddler is less likely to fall out.
The internet is naturally a place where mattress, crib, and crib bedding can be found in quantity. So if you don't see what you want around town or don't need the hassle of running from store to store to find what you want, search online for round cribs, round crib mattresses, and round crib bedding, oh, and happy shopping.