Cots come in 2 mattress sizes:
Standard - 1300mm x 690mm
Large - 1300mm x 760mm
The larger style cots are a great option for twins if you want to co-sleep.

Types of Cots
Cot - Day Sofa
 You can remove the drop side once bub starts to climb
out making it safer for them if they do fall out - not so far to the floor.

Cot Bed - Day Sofa - Junior Bed
These types of cots can be used as above.
You can also remove both sides and in some
designs you can lower the ends when turning into the junior bed.

These are great options as they extend the life of the standard cot.
By converting the cot your child can the first 4 to 5 years in their cot!