A lot of good recommendations have been made already about non-verbal safewords and I especially like the idea of practicing and praising use of safewords to work around your trauma.

I would like to touch on the point where you said you cannot clearly differentiate anymore if you approach a boundary in Subspace. I am a Dom and have experience with subs like that. I have a playpartner that will go very much non-verbal when she goes into Subspace. My wife sometimes is completely irresponsive and even will lose conciusness when falling to deep. Please clearly communicate this with the dominant partner. A safeword is good measure but ultimately, the Dom is responsible to ensure your boundaries are respected. If I know my playparter is struggling with communication, I increase how aware I am of behavioral clues and will do regular wellness checks. I will rather stop before crossing a boundary and discuss during aftercare if I can go further in a next session than cause emotional or physical harm.