An adjustable mobility assistance device providing support for a user on a bed or similar furniture is disclosed. The mobility assistance device may include a base that can fit under a mattress and a support rail that extends upright relative to the base. The longitudinal dimension of the support rail may be adjustable independent of the base. The support rail may be pivotally coupled to the base so that it can be disposed in an upright configuration or a lowered configuration while the base is under a mattress.