If possible buy your next bike and keep the old one for a while. That's what I use to do but now have a family.
I too love the t-bird and really wanted one but could not find one soon enough. I bought a SM and love it but I am still a bit uncomfortable with the foward controls and low seat, my first cruiser. After 14k on my SM I still seem to prefer standard ergos and a taller seat. Thought that might change...maybe not.
What year t-bird did you have? Standard or sport? How would you compare to the SM?