Career in internal audit

hi, 

you can go for course on internal audit, no such experience is required since you are already a commerce gradute, you will not find much problem understanding audit procedures,

Internal Audit more or less includes vouching with deep sense of knowledge of account and accounting standards

Internal audit especially with big 4 would be a good career choice as you will learn the process and business of a company in detail but audit of same client year after year is  boring .but since you have 13 yrs of experience in other field assuming that you are a manager shifting to a different career may be impractical and starting from scratch with less salary try to grow in your existing field all the best