It's been nigh impossible to ride the subway in the last year or so without spotting the ubiquitous ads for mattress startup Casper, which delivers relatively low-priced mattresses in a tidy, easily transportable box. (Indeed, the whole "mattress in a box thing" seems to be a trend in the startup world, if the recent reviews on Sleep Sherpa are to be believed.) Last month, a new competitor, Helix Sleep, entered the fray, and with a twist: Their mattress is entirely customizable.

How it works: You take a quick quiz online outlining details like your height and weight, whether or not you get hot or cold at night, what position you tend to sleep in (side? stomach?), and preferences for firmness. (In a recent test run at their NYC showroom, this took about a minute to complete.) This information ends up as your individual "sleep profile," which is used to create a mattress built to your specifications for what the company describes as four key factors: feel, support, temperature regulation, and point elasticity (in other words, the ability of a mattress to keep your spine evenly aligned).

The big kicker here: If you share a bed with a partner, for $100 extra, Helix Sleep offers the option of a so-called "split" bed, where each side is customized to one person's preferences. While a jointly owned (and personalized) mattress feels like a big and costly commitment for couples to make—prices range from $600 for a not-very-coupley-twin to $995 for a California king, without the $100 splitting charge—this could also spare a lot of agony for perpetually freezing, soft-mattress sleepers who happen to have paired up with a partner that needs extra support and kicks off the covers every night. (And there does seem to be a big potential for variation here: While we haven't slept overnight on a Helix Sleep, when we stopped by their showroom, the ultra-firm preferences of whomever had last visited were a far cry from the softer, more forgiving version the team put together based on our sleep profile.)

Once you've placed your order, Helix Sleep sends your mattress within a week (with free shipping), and offers a 100 night "sleep trial" that allows you to return it after a few weeks should you realize it isn't working for you.

Want to see for yourself before committing to a mattress you've only seen over the internet? Through the end of September, you can book an appointment at their Financial District showroom to check out the goods.

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