Personally didn’t have that much bleeding either time. I got loads of pads and didn’t need them.
Aldi inco knickers for the first few days, they absorbed just fine, didn’t have a problem with these. I also used these when my waters broke. Then the ABENA maternity pads from Amazon which are nappy like in thickness and massive!!! But didn’t need the whole pack. I had the lillets maternity pads which I didn’t rate as they were just really, really long and I didn’t really leak forward or backward so a bit of a waste of time. My favourite were Asda bladder weakness ones. Wide, kind of elasticated to cup but not so massive they’re uncomfortable. Also had some really cheap pads that were like old fashioned sanitary towels I used for like half hour here and there (say between removing one and getting in the shower just while I fed baby).
Overall, I had maybe 5 days of very heavy period type, then 3-4 days heavy period then it just went to normal sanitary towel heaviness before tailing off to need liners. I never needed the length, more so the width. 1 pack of pants, 1-2 Asda packs and just sanitary normal towels and liners would have seen me through comfortably.
I have a waterproof mattress protector anyway but got incontinence pads as I use them as disposable travel changing mats (don’t want to put a pooey travel mat back in the bag). I sat on one in the car but the inco pants contained the leaking waters and though my waters went in bed, I felt something and stood up and then they came so the bed didn’t get it.
Never needed to protect the bed from PP bleeding. But a waterproof mattress protector would be a good shout for PP sweating, possibly bleeding leakage and waters so seems like a good multi use idea. But pads, don’t buy loads in advance, supermarkets or prime sell them if you need them, you’ll never be without.
why am I so excited yet so nervous 
