Solo dev in similar situation here. Agree with some of the other comments that the moat is not the code, especially in OSS.
I'm trying to find a sweet spot between the OSS part of the software and a potential premium feature set that would add enough value that people would be happy to pay for it. The OSS part becomes the validation of user need and distribution; the paid layer validates revenue.
If you couple that with great customer support you give people little reason to switch. In an age where everyone can build product, marketing/sales and customer support seems to be premium.
How we build retention with agents being the primary user/customer is another issue...