You're getting to a more advanced stage with your design and would like to put something that feels quite real in front of users, but you can't afford to build a high-fidelity prototype.

Only make the journey critical parts interactive. Fake the rest with your design assets. It will still look and feel a lot like the real product.

1. Think about the critical user journey(s) in your design (potentially this could be two or three journeys).
2. Think which interactive features would be needed to support this journey.
3. Figure out the simplest way to build the prototype that will provide those features (this could be simple a clickable presentation).
4. Now fake all the non-journey parts of the prototype with flat graphics. (i.e. the designs that you have already been working on). This will be 95% of the prototype.
5. Ensure the interactive parts are working and the journey works.
6. When testing with users, explain that it's only a prototype and there are many things that don't yet work.