That does not mean your son does not have astigmatism. You can get many lenses in the 2-week disposable contact lenses with your son's current prescription. You could even try daily disposables. A few brand names are regular Focus, Acuvues, Seequence and Precision UV's. However, it sounds like your son may have difficulties with contact lenses.
Some people do all the right things and still have problems.
I know your son is at the age where appearance is very important, but what might be worth a try is to not wear any lenses for 1-2 weeks or until his eye feel completely back to normal and then repeat the measurements for contacts and try a different type. Given your son's past history it would be wise to continue to see an ophthalmologist but please ask for the reasons why the doctor thinks this is occurring so frequently. Also, remember contact lenses are often trial and error and what works for one person does not always work for the other. Your son should not sleep in contact lenses even if they are design to sleep in, he should wear them as daily wear. I wear contact soft contact lenses and have recently developed a problem with redness and swelling in my right eye.