i have recently replaced my mattress plastic cover, which fully encased the bed. But over 12 months it started to break up. with the top waterproof layer pealing off in large white chunks. So i have ordered a new one, and a different brand from a UK incontinence site. It is clear, but fitted to my single mattress. I thinkit is important to get the right size, especially if you sleep in a single bed - length and depth. I choose fitted as i dont want it coming off.
I wear plastic pants over my diaper/nappy at night, but sometimes, especially if im trying a new brand, the diaper can become incapable of holding pee and leak out into the plastic pants and then 'wick' out around the leg holes.
The batch of I.D medium nappies i bought, claimed to have a capacity of over 2000ml, but really struggled to contain more than 1000ml. Fitment was bad , as they are smaller than sizing claims. Further more the filling was patchy slightly clumpy in some.. overall a poor nappy that is false saving.. i think worked out at about 42p a nappy.
As for mattress cover i also use fitted bedsheets and attachable elastics to hold the sheet on, which i feel is important as the sheet will want to move on a PVC cover, so one could wake to find the bed sheet has become detacted and not fully covering the are where you lay