Many ophthalmologists advise against swimming in contacts. Their main point is that chlorinated water retained under contacts can cause more damage to the eye because the chemicals are not washed out with tears. But if your wear goggles that do not leak, pool water does not get into the eyes! However, some people still prefer to swim in optical goggles (my H does). Many online swim shops have them in stock. The trick is to find a style that fits your son's face comfortably and stays in place. I'd check with a swim shop in your city and let your son try on several styles to see what he likes.
Here, for example, is the Speedo goggle ( wow, they now make them in a very popular Vanquisher style!): Swim 2000 Inc - Speedo Vanquisher Optical Goggles by Speedo Optical Goggles - Goggles Speedo USA Swimwear
Here is a Tyr one: Swim 2000 Inc - Tyr Corrective Optical Goggles by Tyr
Kiefer makes their own goggle (look for Item Number 690025): Swimwear, Competitive Swimsuits and Swimming Accessories | Kiefer.com
Both Keifer and Swim2000 are reputable online swim shops, BTW.
There are some specialized prescription eyewear shops that make custom optical swim goggles, but they are not worth the expense IMO.
There are plenty of near sighted Olympians and World record holders!