There is a simple way to keep your feet comfortable while improving your pedaling efficiency at the same time. By loosening the straps on your shoes you may find yourself pedaling more efficiently than ever before. Here are some thoughts/ideas and how this can be achieved.
Too often people buy bike shoes that are very narrow and tighten them as if they are wearing hockey skates. This can cut off circulation and squeeze the bones of a foot together causing any number or foot injuries' or at least numb feet. A simple suggestion is to buy bike shoes a half size larger and search for ones that have a wide enough toe box. If you live in a warm climate your feet are going to swell during longer rides so a larger size is warranted, and if you live in a colder climate you need to make sure you allow for extra room for thicker or warmer socks during the cooler/colder winter months. Make sure to adjust tension every hour of riding to accommodate for swelling. Bike shoes are often narrow so a simple shoe stretcher could be used to widen out the toe box if needed.
The best way to start this process is when you doing workouts on your indoor trainer. Loosen the straps a little bit at a time. If you find your feet moving around inside the shoe then you may not be applying force to the pedal efficiently. With practice, you will learn to relax and unweight the foot on the upstroke you find a better connection to the pedal if you give yourself a bit of time to work with this.
Next, do this during your easier road rides. Play with different tensions to find one that feels right. Over time you will find the optimal tension to relax the feet given enough room and allow for optimal power transmission.
You just might find your riding better and more comfortable without numb or cramped feet.