DS2 is 5 months old, and spends his nights in my bed (wouldn't settle anywhere else). I'm going to try and move him into a cot but I'm not sure if it's OK to use DS1's old mattress because of SIDS risk.
The old mattress has a plastic fixed outer, and a removable washable cover. I assumed that would mean that no nasty bugs etc would be able to permeate it. And the cover can be washed at 60 degrees.
I reused dd's mattress for ds. It also had a removable washable cover and the underneath bit was washable/wipeable.
This is what the SIDSwebsite says:
It is very important that your babys mattress is kept clean and dry. Ideally you should buy a new mattress for each new baby. If you are not able to do this, use the one you have, as long as it was made with a completely waterproof cover and has no tears, cracks or holes. Clean and dry it thoroughly. Check that the mattress is in good condition; is firm, not soft; fits the cot without any gaps; and doesnt sag. Never sleep your baby on a pillow, cushion, bean bag or waterbed.