Sit on bikes you are considering and start with any bike that feels really comfortable. Getting a bike that is too big, or too small, and that includes the weight of the bike, the height of the seat and the reach to the bars, is just looking for aches and pains later on. Unless you are a speed freak, even a smaller displacement bike can do the job, but generally larger engines, running at lower rpm, will be smoother and more comfortable for riding (especially at higher highway speed). If you plan on having a passenger much of the time, make sure you have a decent passenger setup, including more than a mini-seat and ideally a passenger backrest and something to grip on. Lots of bikes today have ABS, and this adds a nice safety factor, especially if you ever have to really grab the brakes to stop in an emergency. And you can add a windscreen and nylon or leather bags to almost any bike. Hard bags that lock are ideal, but if you are not making long trips often, textile or other non-locking bags work fine (not too many people mess with other people's bikes. I've left my bike overnight at motels many times with leather bags that cannot lock and have never had a problem.)

Right now I ride a Triumph Thunderbird. I'm 71 and not as strong as I used to be, but I find this bike easier to handle, even at low speeds, than some lighter and smaller bikes that I have owned. Used Triumphs may not be easy to find, but any of the cruisers are a good choice for you: Thunderbird, Storm, America, Speedmaster. Star (Yamaha) makes some nice cruisers, as does Suzuki. Personally I like these better than the comparable Hondas and Kawasakis. Any of the Japanese brands will cost less than similar HD's, and in my opinion, are a better value and choice.

Good luck and safe riding.