google youtube for slip knots and carry chest to chest in a one-shoulder carry.

the knot probably wouldn't be an issue, it's the strength of the fabric that is the safety issue. comfort wise, you will be better with something with some diagonal stretch so it moulds around you and baby. a purpose-woven wrap will be heaps more comfortable for you and baby, but a sarong may well suffice. You just need something tough enough to stand up to some pulling and yanking, as well as the baby's weight.
There are some fairly cheap wovens around 2nd hand, if price is your concern.