Thanks for the response. Yes- with the 40" of vertical space I would only put some carpeting down (that's less than an inch) and the mattress with no platform or frame. I can't seem to find examples where the amount of headroom in the loft space is listed or shown. All I found was a single Yahoo!Answers thread where one person said you need 36" between the top of the mattress and the ceiling. Here, I would have about 28-30" depending on mattress thickness.

If you only use your bed for sleeping, you might be okay...
Also think about how quickly you or your back will tire of negotiating that space every time you make the bed. You'll be on your hands and knees whenever you strip bedding and remake the bed.

I know. As a designer, would you advise against this, or do you think it's workable?

You could sit on the floor and measure the distance from the floor to the top of your head - that would give you an idea of how much room you need to get in and out of bed. 28" - 30" is really not enough and might feel claustrophobic.

How about using that space for storage and getting a murphy bed or hide-a-bed downstairs instead?

So, what is going on in the main space that makes this the only logical area for sleeping? Can you post some pix, please?

The apartment space is beautiful and I think would lose all reason to get the apartment if the loft space isnt workable for a bed. I would just go with a different apartment rather than use the loft as storage. I otherwise love the apartment, but very concerned that I will be frustrated with the height of the loft.

If you think you'll be frustrated with the height, then you likely will be. I know I wouldn't be able to do it, but I'm not as flexible as I was 20 years ago. If you're young and limber, you might be able to tolerate it for a while.

Yes, it is very little space and you basically have to crawl, or roll into it every night.
You could make a space like that now for practice and see how it feels.

Is this close at all re: headroom? I Googled "loft sleeping area". and found these. What are the dimensions of the floor? Would there be ample space around the mattress to crawl?

The storage steps lead up to the loft.

Those look close in terms of vertical space, yeah. Though the loft in my potential place is much larger; i.e. could fit two queen size beds. Not that I would know what to do with any of the rest of that space given the height. Thanks!