If I were you, I would break down my investigation in two buckets:
- Find product similar to yours, and learn more about them
- Find publications, reviews and launch notes of these comparable products
- Use the above analysis the create SAM or Serviceable Available Market
- Define Personas that exists in this SAM
- Identify the Persona that your product is serving. If you can't find your existing customer segments in this above list of Personas, then you don't have a product market fit.
- Run NPS (Net Promoter Score) Survey. This is almost a gold standard for receiving feedback from existing customers. Note that only a handful of your DAU (Daily Active Users) will take the NPS Survey
- Run more detailed survey with existing customers or users to gain detailed insights on which feature are the most appealing. Always, include a free-form text box in any survey for gaining qualitative feedback from the survey respondents. The responses in these text fields are great material for opening your presentations to executives
- Do User Interviews with early adopters of your product to gain their insights. Note that this is not to find the next set of features to implement, but more to find what works best for them
- Stretch Goal: Do Focus Groups with multiple users (>5) with a goal to brain-storm about your product
Surveys are not the only tool to get a pulse on your customers. You have an army of options, and you should use multiple options to get an accurate insight.
Final Note: Pick and choose from the above list. There is a cost of doing any analysis, and you should stop when the cost exceeds the benefits.