Thought i would post this to help members out who are looking for a realistic highchair suitable for adults. this site in the US has some ready made ones that appear to have the right size. Especially the wooden ones.
However, they will custom make to your requirements. And i think if you asked for standard pine in kitset form, the price would dramatically reduce.
the site is Highchairs | Baby High Chair | ABaby.com
I hope it will be of help to someone on here.
ps. Also, if anyone want custom made bibs or clothing, i can put you on to a lovely lady in the USA who will make anything you like.