When does a toddler bed get babyish?

[Hadeley]

Such a dumb question but: we are considering buying a floor bed for our 1,5 year old. She is young, but precocious and determined, and she has started trying to climb out of her crib, so we think it's time. We have our heart set on a montessori floor / house bed, because it feels safe (considering her restlessness and climbing antics), cosy and just because we like the look of it. It's a bit of an unnecessary expense because we could just get her a normal single, but it should last her quite a while because she is small for her age, and it has a 160 x 70 mattress. The only thing that worries me is that even though it suits her now, she will find it babyish way before she technically grows out of it. She is still more or less a baby now, but how will she feel about a floor bed like that at age 6 or age 9?

Any advice?

Can you just put a single mattress on the floor and then when she's older put it onto a bed base. That's what we did with my daughter when she was nearly 2 and I was worried she might fall out of bed.

Depends on her size, what percentile is she? My 2 year old is 99th and we are getting him a single bed in a couple of months, he is in a 140x70. It was his cot but you can take the side off so that's how he has it atm.

Why not just a mattress for the trannsition from cot to a proper bed?