For staying at Mumbai Central, you can book Urban Pod at 1st floor of Mumbai Central station. The booking process is same as that of retiring room on irctc tourism site. Can be booked offline too (if available).

PNR no. is mandatory.

Best...
more...

thing is check out time is 12/24 hrs. You can check in at any time and book for 12/24 hrs slot (not fixed like RR whose check in is at 8 am & 8 pm).

Costing:
Private pod - 1300 appx (12 hrs), 1900 appx (24 hrs)
Classic pod - 800 appx (12 hrs) 1200 appx (24 hrs)
(including taxes)

Difference is in pvt pod you get own room whereas in case of classic pods, its like a dormitory but privacy is there too. You can close your pod door. In pvt pod l, you can keep your luggage in your room, but in classic pod there is no such place & you'll have to keep it in lockers present outside the pod. (check out youtube videos for same)

The washrooms are common, unisex, but in abundant nos. and very clean. Cleaned at regular intervals too.

NO FOOD is allowed inside. Water you can take in your bottle or buy from the reception. For fooding, there is Comesum on the ground floor or some hotels/eateries are present on Belassis Road outside the station.

Shoes have to be kept in lockers provided near reception.
Inside pod, adequate lighting, AC, air outlets, TV, headphones, charging points (usb and 3 pin plugs) are present.
Overall a very good place to stay.
(The pic in the blog is of pvt pod)