What size to choose for plastic pants?

Hi all,
I have decided I wish to try some plastic pants and have found some on ebay. http://www.ebay.com.au/itm/3-pcs-ADULT-BABY-PLASTIC-PANTS-PVC-incontinence-P005-/201952673967
I fall right on the border line of the small size according to their chart literally my measurements are like 1 inch below the maximum. So I am not entirely sure which one I should get a small or medium. I want it to snug not too loose which is my concern if I buy the medium as I would only just be over the line for that however I don't want the small to be digging into my skin because it's way too tight. What would people who have some experience suggest?
Thanks.

For you, mediums would be a good bet. If it feels tight, the sides could rip and make leaks more likely.

I use Haian brand and I find it better to have the plastic pants just a bit larger than my actual measurement. I believe that a Small would be very tight. By the way, I like this brand of pants, too.

I bought exactly my size once (on the edge for small vs medium) and the leg holes cut into me really hard. I buy medium plastic underpants now and they still work great and fit well beneath my jeans and over my training underwear normally. More sites now can classify not only the waist size but leg hole opening sizes which is great for me to make a good decision.

Thanks everyone for your help. I bought the pink medium ones and excited to try them I would of bought small but after everyone's else's opinions I think medium will work better.