Hi drumster --- Whenever I embarked on fitting new kitchens in the past I used the old fashioned method of precisely measuring the kitchen in metric measurements, because the units are usually supplied standard as metric, and positioning doors, windows and obstructions plus services on a detailed scaled plan drawing of the kitchen dimensions.
Once I had these exact scale drawings on graph paper, I would make further copies of the floor plan and layout standard sized base units which are usually 600mm wide single or 1200mm double, all around, or better still pass them to the wife and tell her to mark preferably where she would like things to end up. If technically possible I would then decide on the layout of wall units and galleries above the floor standing base units and worktops, with that worked out I would tell her to pick her units and worktop finish from the catalogues I would acquire, along with style of sink fittings & appliances she would like incorporating in the kitchen.
Once I knew how many sized units of which style, size and finish would be required, we would get catalogues from MFI, Howdens, B&Q, Jewsons or wherever indeed takes your fancy, then once you select everything price it all up one by one until you have a price for the complete fittings that you will need to fully complete the job.
At this point I would go into the store ask them if everything was available from stock or fairly quickly, then I would tell them what I needed and really stick at them until I managed to get a great price reduction for the whole lot delivered on a certain day, to which I would have a pre-arranged joiner friend of mine ready to rip out the old and start fitting the new units, this joiner friend would either work on a daily fixed rate or give me a complete fixed price for doing the total job whichever reasonably worked out to be the best method.
You may find this is too much for you or you do not want to get too involved, but you can save a lot of money doing most of the organising yourself and cutting out the expensive middlemen or companies, to get the same or even better results if you plan & price everything up really carefully beforehand.