A minecart, which behaves exactly like the standard minecart (you can ride in it), only when it is night, it qualifies as a bed and it doesn't set your spawn.

Should I use a carpet for the bed, I wonder?

Will close this one for now as it is already in code.

It turns out that this cart needs a lot of hack, but I've at least done most part of it.

@CovertJaguar Can you decide how should player sleep and leave the bed?

I'd not name it sleeper, for sleeper means railroad ties in British English.