Yup, the WFP's will post .................
But ......
Ladder mats.
They are black rubber about 8 ins by 4 or 5 ins wide with bobbly bits all over them and they come in 4's and you can use 1, 2, 3 or 4 together and all 4 are about 2 ins thick. So each one is maybe adds half an inch.
They are the dogs wotsits for leveling ladders and ours cost about £25 and we use them day in and day out.
I really recommend them. (or how ever that word is spelt - rather like the word 'commitee'' or however that's pselt)
Almost all cleaning suppliers sell them.