Oh yes I was referring to wheel size, I thought that was how the Whizzers were advertised. I don’t know they went by frame size. I have trouble lifting my leg over even smaller bikes, so I am always looking for something lower to the ground.
By Whizzers do you mean cruisers? Whizzers were motorized bikes proudeced many years ago. There are still whizzer replica kits out now.
If you're talking about a cruiser only the higher end ones sold in reputable bicycle shops will come in frame sizes. As for department stores bikes you get what you get in frame geometry for a particular model. The good news is the different models can have different frame geometries.
This is where the calculator I posted comes in handy. It can give you a general idea of what you'll need in a (seat, top and down) tube measurements. Once you get close to the best frame proportions for your particular body build the handle bar height and angle along with the seat height can be adjusted to give you the best fit.
It's important to get a frame designed to fit you and has been adjusted for you. Riding a frame that doesn't fit you means if you ride for any distance it's going to be a painful experience.
To add to comfort levels I recommend 2" wide road slick tires, front suspension and an adjustable suspension seat post.
Of course you could always go for a stretched frame or recumbent build.