First, congratulations on your commitment to reducing your weight. You may be the ambassador for others to do the same after they see what you have accomplished. If you want to really feel good about how much you have already lost, put a backpack on with the equivalent weight. You have accomplished a tremendous achievement already.
Your ride...I don't think that shifters would give you what you really want - a new bike. Why don't you make it a goal that after you lose 90-100 lbs. you can reward yourself with a new ride? You have earned it.
Just a thought.