How much storage does an ottoman bed have?

Roughly 200 litres on a double and 270 litres on a king. That is enough for spare bedding, off-season clothes and the suitcases that otherwise live on top of the wardrobe. Depth is usually 30-35cm under the mattress, so taller items have to lie flat.

Are ottoman beds easy to lift?

Modern gas-strut ottomans lift with one hand at any size, since the strut takes most of the weight. Older spring-strut models are harder to lift and the springs wear over years of use. If you are buying second-hand or a budget model, check the lift action before committing.

What's the difference between an ottoman and a divan?

An ottoman has one large compartment under the whole base, accessed by lifting the mattress on gas struts. A divan has small fitted drawers in the base side that pull out. Ottomans store more (200L versus 85L on a double); divans are easier to access for daily items.