Under bed space - making the best use

[ZenNudist]

Ds is only 3 but about to change his nice low cot bed back into a cot for new baby.

I want to get a single bed for him and weighing up options for either an extra pull out bed or underbed storage. A plain bed frame would be much cheaper but would it be better to get something more suited to the long term?

What works for other families?

Are pull out beds any use? We are a few years off sleep overs and could make do with a blow up mattress.

Built in storage also pricey. We have decent amount of storage already but suppose its useful for towels or bedding.