I would also consider a young architecture practice. If you explain exactly what you want - they will help you design something for your specific needs, especially if you want to self build.
In the recent years there's been an amazing amount of fresh young practices like Assemble (although I'm not sure if they will be more expensive since they've won the Turner Prize), Practice Architecture (who actually engage in the physical building process themselves), Becoming X (who make these extraordinary paper models for their clients to play with and re-arrange to find the perfect lay-outs), there's also Assorted Studio, We Made That, Pupp Architects. Let me know if you're interested and I can PM more suggestions, I'm an architecture geek. 
All of these have graduated from world leading architecture schools like RCA, AA, The Cass etc. and are practicing 'alternative' architecture, which is far more user friendly and less prescriptive to 'traditional' architects. You can also stroll through their instagrams to see if their style/vision 'click' with your aspirations and even though most are based in London, they work all over the world.
I would also look at Walter Segal for inspiration - an amazing architect who designed a self-build system - for a couple to build their own house without having any prior construction experience. There's a little street in London with these self-build houses called Walters Way - it's very sweet.