i like batiks for pillow cases- our normal quilting cottons have a thread count of about 60---nothing close to the hundreds used for sheets/pillowcases in stores-
for soft i go with flannel- for regular cotton i go for batiks- which can have 100+ thread count.
pretty much any 100% cotton will soften & just get (cozier) with each laundering- it is the nature of the cotton fibers- poly blends do not soften with age- they stay the same as they are in the beginning. i love muslins when i want something that is going to be wonderfully soft after laundering- and they dye beautifully too- i often will pick up a bolt of bleached muslin then dye it to match quilts/projects i want to accessorize