I recall a student of mine in Parsons arriving with a very similar material to domette she picked up at Joanne Fabrics. This must have been the same stuff.
I've known tailors to use pocketing or even muslin in place of domette. Many maintain its just to cover the chest piece and add structure to the chest area.
Go along to your local sewing centre/fabric shop and see what they have in the way of suitable interlinings. Interlinings tend to be fluffier, so should work as a substitute. Look for cotton flannel or cotton batting? Try some samples to see how it handles.
Personally, I need to literally touch/feel interlinings to get an idea if they're suitable. Often when I've bought stuff on eBay/online without first ordering a sample (usually because this option wasn't given), I've ended up with junk.
Curtain shops also sell Domette, BTW. The thinner end of things, but that's fine for a summer suit (you can always double-up the cloth if too thin).
Pick up some cotton batting used in quilting, its essentially domette.
I've known tailors to use pocketing or even muslin in place of domette. Many maintain its just to cover the chest piece and add structure to the chest area.
Go along to your local sewing centre/fabric shop and see what they have in the way of suitable interlinings. Interlinings tend to be fluffier, so should work as a substitute. Look for cotton flannel or cotton batting? Try some samples to see how it handles.