The extent of market research depends on the nature of the acquisition and can be somewhat subjective. In fact, you already stated the basis for your market research in the background to your question. You will need to document that contract file with how "...market research indicates other companies’ similar products, or products lacking the particular feature, do not meet, or cannot be modified to meet, the agency's needs" [FAR 8.405-6(b)(1)]. A concise paragraph on how you made that determination, so that a reviewer can follow the logic, should suffice.