Have you thought of just putting a different seat on the T100? They sell seats with lower profiles that are narrower in the front (which REALLY helps if you have shorter legs). I sat on a showroom T100 and felt the same way you did… Then I sat on my friend’s Bonnie with a Corbin seat and it felt 100% better. It was like night and day.
He’s got this seat (http://www.corbin.com/triumph/bonnevillegnl.shtml)
There are also other options like shorter shocks/springs that can take it down an extra inch or so, but that’s a rather expensive options (and it decreases your lean angle in the turns).
Try asking questions (or just searching posts) on http://www.triumphrat.net. Friendly folks and there’s a wealth of knowledge. For seat options, you can try http://www.corbin.com or http://www.british-customs.com.
Also, your dealership is probably associated with a R.A.T. club (rider’s association of Triumph). Find out when they meet and show up. You’ll probably get to see dozens of bonnies there with different seats, configurations and customizations as well as get an earful of advice from the owners…
Hope some of this helps.