bolster

nouns

a pillow that is often put across a bed underneath the regular pillows
bolster, long pillow

verbs

support and strengthen
"bolster morale"
bolster, bolster up
prop up with a pillow or bolster
bolster
is a type of (narrower)
support by placing against something solid or rigid
"shore and buttress an old building"
prop, prop up, shore, shore up
add padding to
"pad the seat of the chair"
bolster, pad