OK, here is one case where size really matters. Beds are usually bought based on the general rule of thumb that it must be the biggest bed you can fit in your room. Remember that size should not only be based on width and height but also the length which should ideally be 10-15 centimeters longer than the tallest sleeper. Those who are over 6 feet in height, may have to go for customized beds but if you search diligently online, you should be able to find bed manufacturers who make beds up to 7 square feet or cater to other special size requirements.
Your second consideration should be support and comfort for your weight and build. Good and proper support is determined by the coil springs inside the mattress and should be conducive to proper spine alignment. You must be able to try out the beds by lying on them for at least 10 minutes, getting a feel of how firm the mattress is. When you lying sideways, your spine should be straight and when you lie on your back, your spine should maintain its natural curve. Do as Goldilocks did and choose a mattress that is not too hard, not too soft but just right and according to orthopedic experts, that should mean the firmest and most supportive mattress you feel comfortable in. Try your usual sleeping positions as well as a few tosses and turns. If it is going to be a bed for two, you should go for something larger and one that minimizes partner disturbance and should enable you to lie side-by-side, with your arms behind your head and elbows out but not touching.
