a step thru is not really necessary. You can be shown how to take a standard top tube bike and lay it down, then straddle the bike and pick it up. You should not be able to sit on the saddle and reach the ground on any bike that is properly set up for riding. If you can reach the ground while on the saddle, the pedals are not set up right and are putting unnecessary strain on your knees. If I am misunderstanding what you are saying, my apologies.
Test ride the bikes you are considering and get the one that feels the best to you.