I don't have any first-hand experience, but here are someconsiderations:
Oilcloth is heavy! You need a sturdy foundation fabric that can carry the weight without just ripping. So a lightweight (like 70 g/m2) blouse cotton is out of the question. OTOH using a very thick and heavy fabric adds even more weight to the finished oilcloth without any positive effect.
As a rule of thumb:
- The fabric should be woven tight enough not to have any visible holes (like muslin or cheesecloth).
- The fabric should probably be woven in "canvas weave" (one thread goes over on, under one, over one, etc). Other weaves like twill or satin have one thread go over several others, under one or several, over several etc. This gives water more opportunity to seep through.
- The fabric must be thick enough to not rip when it's oiled. Something like old bedsheets, tablecloths or tent canvas should do fine. Denim is already on the heavy side of the options, outdoor tarp or furniture fabric is probably much too stiff and heavy.
All things considered, I would probably use a 100 - 130 g/m2 cotton instead of a heavier canvas.
PS: Although oilcloth was traditionally made with beeswax and/or oils, modern alternatives use simple construction silicone. It's extremely flexible, water repelling and more lightweight than traditional oilcloth. If you're interested, here's a YouTube video by NightHawkInLight (not affiliated).