that 22-thou/washed is still the same compressibility as 15-thou unwashed. don't sweat it.
if you have any unwashed ticking left, just cut it in 5-colored-stripe strips and use it as-is.
you might also go down to (most any) fabric store w/ your micrometer and pick up some 18-20 thou ticking (standard-as-issued) for a tighter fit. Denim also works well (comes in different weights/thicknesses) but doesn't come with it's own Cut-Here straight lines.
PB/48 twist can be fine -- just keep load mid-range.
Oh... and run a
damp patch in/out/in/out between rounds....