I recently tried to become my own ISV. I produced the first draft of https://conciergeapp.uk/ within 2 weeks after a chat with someone who is in the Facilities Management (FM) section. Initial interest in the market looked good and I had plans to make a modular platform. After some refinement etc, I totally failed to sell it. I tried so hard but it was exhausting. Then I got a regular job, but still.. this does appeal. Wish you luck! The hard part is not the coding.