Melodie, I respectfully have to inform you that I know of no good option for you to get to Belize without flying. Would you be traveling alone or with another senior?
Over the road would probably not be a good idea for a senior. There are plenty of stories about the adventure of traveling to Belize by road but I would be reluctant to suggest that for you. Maybe there is a bus all the way but I think that may not be the relaxing trip that you would like. Lan Sluder would know more about this I would imagine.
Sailing here is done often but I don't think you meant "sailing" like on a yacht. There are freighters who come to Belize City and they might carry a few passengers. One time I was going to take one from New Bedford to the Azores, I don't think that particular one runs any more but there might be one out of Florida to Belize. Anyway that could also be a problem because you need transportation both ways and they are generally only in port a few days. There are cruise ships which include Belize as one of their stops.
I had some wonderful times years ago in Ensenda and I understand it is nice in Cabo San Lucas. That might be a little more do able for a person with your needs. Belize is great and especially San Pedro but it can be a little rugged and personal comfort at all times should be a concern for you. I wish you luck and hope that you can find a safe way to make it to Belize. Iíll be paying attention, Iím somewhat hard of hearing now from working in noisy power plants all my life and Iím getting along in years. Be careful and good luck again.