May I suggest this...I'm VERY new myself, but because of my profession I find that I often get lost in the voice of the dominant. It is really helpful for me to try a positive word to see if I will be able to remember it when I need it.
For example, saying edge...when I am right on the edge... (gives credit to someone else for this difficult but useful tactic with a smile and nod.) Being an intelligent woman I thought "how hard can that be?" When I needed it...I was racking my brain thinking what is that damn word!!!! I finally said "the word the word" lolol!
I can totally see where you might, if in sub space (though I haven't experienced it) feel the same, or even just simply forget to use your word. I don't plan to be in a place that I would consider sub space until I can trust my dominant to be able to tell the difference both with, and for me. I recognize that everyone is different, and that over time and with practice of a word I may learn it much better and have better control of its use. I just don't intend to rely only on the use of a single word for my safety. I plan to have one, I plan to know it...but I intend to PLAN for safety as well.
For me that means taking time...not a week, not a few weeks, a LOT of weeks, months, etc. to get to know someone so that we can understand each other before meeting. And even in an o/l only relationship, I know that I want to be able to feel as comfortable as I would in r/l. For that reason I like to spend time talking about things OTHER than bdsm.
Certainly all of the things said above are true as well, and I wouldn't enter into a relationship without knowing them, looking through a list with a dom, starting slowly...and I wouldn't even be thinking about a collar yet sweetie...start thinking about the person.
Just my advice, take it, leave it, use what you can! I never knew what might help me, and I thought maybe my experience would shed some light for you.
Best wishes and enjoy your search.
Nei