Something to consider – presumably Snugglebundl didn’t get a clearance. If they had, HMRC would have told them to charge VAT. So although they had to go through the tribunal process, they’ve ended up with a better result than they would have got from a clearance. For your product, being the designer should enable you to demonstrate what it has been “designed as”. If it has been designed as clothing, looks like clothing and is marketed primarily as clothing, you may have a strong case for zero rating anyway.
The clearance route would be most appropriate if you still have real doubt over the correct VAT treatment. I believe that to get a clearance you do need to explain how you’ve considered existing guidance and that still leaves the correct treatment in doubt. If you don’t hear from anyone with experience in children’s clothing clearances on this forum, your accountant might have contacts who could recommend someone.
For completeness, there is a third option – HMRC have a Written Enquiries Team that you could contact. But I suspect they may just refer you to the two pieces of guidance that I already have, leaving you to decide for yourself how they applied to your product – if so, that won’t really help.