I strongly recommend a decent material, as you will find it difficult to "prove" fireproofing...
The ideal is a material that is IFR - inherently flame retardant - such as wool serge. Wool is a marvellous material as it is naturally protective. Cotton is not, and has to be treated.
You can also get DFR and NDFR - durably flame retardant, and non-durably flame retardant. With the correct paperwork, these are ok. Display felt is a very cheap form of NDFR material (bought from the right place) but it's ability to withstand flame wears off with time.
I always have my drapes just kissing the floor. Nowadays there aren't the cigarettes, and also, they're fireproof, so even if there was delighted cigarette, they're not going to go up in flames! I can't tell you how many black borders (the horizontal black drapes over the stage) I've seen have eight inch diameter holes neatly burned through them, because someone's flown an LX bar in behind it and then powered the lanterns up without checking. Leave one on for a few minutes and it will burn right through..... it's why fireproof materials are so vital. Any dust in the blacks however, will burn easily and start a major fire.
A company like JD McDougall will either sell you the materials or make up a cloth to your specs.
https://www.mcdougall.co.uk/fabric/fabrics/display-felt/
https://www.mcdougall.co.uk/fabric/fabrics/wool-serge/