I definitely prefer a flat, firm surface and usually take my ironing surface to workshops I teach so students can feel the difference from the regular ironing boards they supply.
I make mine with a thin sheet of plywood or pressboard, covered with a large plastic bag, then a layer of cotton batting, then a layer of the silver ironing board cloth which one can buy at Joannes. Mine is about 36" x 28" and sits on one of my sewing tables.
Jan in VA