In your situation, I recommend using an actual 5.5 or 6 ft. bo outside most of the time. The full range of motion will serve you well. In the 270 degree turn and other problematic areas, do you best on these.
I would also practice inside with your Jo when you want to. When you take your rank exam, demonstrating Bo form 2 once inside your garage with the Jo, and once outside with your Bo. Thank you for making me fully aware of your balance situation. As your grading instructor, I like to know your abilities and potential challenges before you even test, so that I can fairly evaluate your performance based upon these parameters.
No two students are alike, and I think it is only reasonable to take into account things like this. I am also still learning more about trying out Jo, escrima, and other lengths — as for the last 10 years I have mainly used a 5.5 or 6 ft. staff. I look forward to more feedback on this.