Bolster is a catch-all term for any cylindrical pillow, used to support various parts of the body during rest or relaxation
Commonly used for yoga to hold postures as well as for sleep

Long Premium Bolster Body Pillow (Small Double-4ft) – 100% Virgin Hollowfibre Filling - Comfort Pregnancy Maternity Orthopedic Soft Support for Side and Back...
4.0
Amazon.co.uk

Utopia Bedding Bolster Pillow (Double, 4Ft 6 Inch), Full Body Pillow, Soft Hollowfiber Filling, Long Pregnancy Pillow for Maternity Support and Side Sleeper...
5.0
Amazon.co.uk

ARLINENS Virgin Extra filled Hollow fibre Bolster Pillows for Maternity Nursing Back and Neck Support (Single 3ft)
4.0
Amazon.co.uk