i believe that a fitted wardrobe should be hand made not mass produced
Everything is manufactured to order in a factory and not be governed by standard sizes, so if you wanted new furniture or just reface the doors, it should be able to be produced, the door style and size just for you.
Removal of your old furniture and taking it away part of the service i would expect (some company's don't) cabinets are made using 18mm mfc including the backs in a colour that matches your door choice or choose to have polished veneer.
www.yorkshirewardrobes.co.uk is one such company