It is possible to boom without cans... Here in Europe, this was (or still is?) pretty common. We filmed a few short films and documentaries with a boom operator who didn’t use headphones. Only the sound recordist (me

) wore them...
It was much more important that the boom operator understood what was being shot—the lenses, camera angles, lighting—and to watch out for reflections and the shadows!! (You know what the boom operator's anthem is? "Shadow on the Wall" by Mike Oldfield

).
You should know how voice projects, what’s happening in the scene—you have to check the script to understand the movement, the dialogue, etc. Communicate with everyone—the sound recordist first, but also the DOP, director, director’s assistant, etc., if you need to clarify something quickly...
There are also rehearsals, and you can practice your boom choreography during those.
On a low-budget project with the gear you described, and mainly being indoors in a small location, I wouldn’t overcomplicate things. Check the sound during rehearsals, understand what’s going on, and learn how your movement and different mic positions affects the sound. In your case, you’ll have to coordinate with the cameraman—do a few passes with you using the headphones to get used to the space, or do test recordings and review them...
Anyway, knowing the capture characteristics of your mic well, along with everything else I mentioned, makes it possible to boom without headphones. For example, you know you have to aim from about 1.5 meters away, with the closest being half meter in closeup shots or soft spoken dialogue (for instance, you set the gain for this distance), and you know the positions to aim from and at.
Then, after knowing where the ideal sound capture happens, it’s only important to avoid being in the shot—whether it’s you, the boom (the cable, the pole, the mic), your shadow, or your reflection... Also, avoid aiming the boom at loud background noises, and try not to change positions too much during dialogue, so you don’t get drastically different background noises. If there’s static noise, that should be avoided anyway, if possible...
Good luck!
P.S. It would be much easier to borrow a separate recorder and maybe even some nicer mic - like MKH50 for indoor dialogue - and only send the feed to the camera for reference, you monitoring the recording yourself, being sound recordist and boom man at the same time...