It sounds like you really want or need to be making money from this venture quickly and that you are either at capacity or nearing capacity for you to continue self-funding this. If I'm reading the situation correctly, an investment in building out a freemium version is not feasible at this point. The cost to do so and the relatively low conversions from free to paid, make this option seem unrealistic at this point, although it certainly has long-term value.

I was able to raise a small angel round from great angel investors at a time when I had a few large companies in varying stages of piloting my software that was all about collecting feedback from employees. So it's possible that you could put yourself in a situation where you could raise a small angel round as well. I would suggest that's the best path forward unless you think one of your customers is near the point where they could make a significant purchase in the next 30 days (which still would mean you're probably 90 days out from being paid).

Happy to talk to you in a call to explore your options more thoroughly.