Later period flint rifles in general, post 1800, and really moreso post 1820, tended to be slim in overall architecture.
I am biased,
but any of the southern mountain style (such as East Tennessee, Gillespie of North Carolina, southwestern Virginia, etc.) of rifles of the late flint era, 1820s-50, can look really nice in a slim sleek rifle. Check out Dennis Glazener's website for some information on Gillespies - I have seen some dandy small caliber rifles made up along those lines.
Also - check out the Contemporay Makers Blogspot and you will find some recently posted nice slim rifles.
That being said, there are some wonderful Pennsylvania styles that will work too - I will let other more knowledgeable of them offer suggestions.
Good luck
Guy