Your regulators are the most important piece of equipment as they are your life support system underwater. Regulators are “one size, fits all” so there are no special sizing requirements.
When looking for a regulator you need to think about what style of diving you will be doing, diving in cold water requires cold water regulators, diving in warm water can be done with cold water regulators however some brands offer specific warm water regulators that are lighter for travel. Having your own regulator will make you a better diver as it is your responsibility to maintain and care for them. It is recommended to get your regulators service annually or after every 100 dives as this will ensure they are in proper working order for when you dive.