Newbaby's bed - need to waterproof?

[lotsofpeas]

This is probably a very silly question, but as a first time mom-to-be, I'm really confused about this
I'm getting things ready for the new arrival :) and would really appreciate advice about the baby's mattress.
We have ordered the Stokke Mini bed, with the mattress. The mattress itself is not waterproof. Of course, the baby is going to be sleeping in a nappy, but what about the inevitable accidents and leaks?
Do I need to get one of those rubbery flat sheets to put between the mattress and the fitted sheet? Or would that prevent the baby's skin from breathing and make the baby sweaty? Maybe a layer of towel between the mattress and sheet would work?

I use Hippychick waterproof sheets (you can get them on amazon), they are designed for children, breathable and not in the slightest bit rubbery or plasticy. My DS is 9 mths and we haven't had any leaks/ accidents as yet so can't vouch for now good they are but they have v good reviews on Amazon.

It should have a casing thing that will be good enough for baby sick (trust me I had the world's pukiest baby first time round!). Any leaky wee/poo will hit babygro and grobag first so mattress will be fine as it is.

The mattress is likely to have a machine washable cover. I would be amazed if wee or poo manages to escape nappy, vest, babygro and grobag, but if it did then you can wash the cover. If baby is sicky pop a towel under the sheet.

Thanks for the advice ladies :)