Please for give the direct self-referral, but I would love to help you if I can.
Space planning family homes is my passion, and I have been doing so for over 10 years with my company (olbc.co.uk). As you suggest, I am not a qualified architect (I use one for surveys and plan mark ups), but I am an interior designer with a very hands-on understanding of construction through my company, and therefore my designs are naturally cost-engineered from the outset.
I have designed dozens of basements & other extensions, as well as entire house redesign, and technical considerations including space planning / problem solving and designing kitchens, bathrooms etc is a particular strength of mine. I also studied at the Architectural Association in the Conservation of Historic Buildings and so I can assess older period properties and make the most of what they have to offer, as well as modernising for 21C life. My ethos is to extend and remodel period homes to maximise their original elegance and ensure contemporary additions still compliment rather than fight the existing.
I have recently completed the floor plans for a listed villa in St John's Wood with a 16m swimming pool in the basement extension, and another GII* villa in Kensington for a repeat client, but I am equally at home and enjoy working on and size domestic home, as most families have the same issues no matter what size their homes is!
If you need any planing permission we have a 100% success rate for obtaining consents. I can also provide engineering, and offer recommendations for excellent party wall surveyors. We can also provide regular interior design services on top if that is of interest.
As a Wandsworth mum of 2 (aged 5 and 3) I'm pretty well qualified to understand what other families need, and this is my absolute favourite part of the process. It's my job to fully understand the property, how you use it, what works / doesn't work, in order to come up with a range of solutions, hopefully some you haven't considered. At the very least I can be a sounding board to run over your ideas and then finesse them into plans to build from - I will challenge assumptions and offer alternatives, though obviously the final call is yours.
Although my company does the full construction service too, I'd be delighted to assist at the early stages with absolutely no assumption of undertaking the construction work, as these are entirely separate services.
If you'd like to meet I can pop over one evening to chat through your ideas and come back to you with a proposal?