I fit kitchens supplied from all the major high street and online retailers- in fact I was a subcontractor to Wickes for 5 years .
Nearly all of the suppliers provide a free planning service.
Howdens and Benchmarx supply to trade only however you if you would like to use them you I can give you access to their trade accounts.
DIY kitchens do not provide a planning service but they have an online 3D planning tool and give advice and can check plans before you place an order.