Loft Conversion

[Robin's Nest]

We are currently planning a loft conversion and require some independent plumbing advice. We have a conventional boiler which was recently installed to allow for extra heating demands due to the loft once converted and do not wish to change this. Once the conversion has been completed there will be four bathrooms – two with a bath and power shower, one with just a power shower and the fourth is a cloakroom with just a toilet and sink. There is a large vented heated water tank in the airing cupboard and in the loft there are three cold water tanks, although these can be moved to another loft area which is not being used for the conversion. We do not wish a combination boiler, due to difficulties when using more than one hot water outlet at the same time together with the loss in water pressure when other demands are put on the system. Also I understand you cannot use a combination boiler with power showers? Given these criteria what plumbing system would be best suited? Is it possible to use either a pump or even a second boiler? Many thanks.