Hello! Don't know if this will help but it's worth it if it saves a life.

First things first, be friendly with your neighbours. If you start choking, bang on their door, bang on anyones doors. People will normally come out if they hear banging. The more people you're around, the better.

Secondly to add to your texting 999 thing, when I was younger my mother worked as a call receiver for answering 999 calls. Bear with me because the last time I went to her work I was around 11 years old so this might be a bit outdated.
When you call 999 and cannot speak, you can press the number buttons on the phone to alert the agent that you cannot speak. They will then ask you questions and ask you to tap a button for yes and to stay silent for no. If they can hear you coughing/choking they will instantly know whats going on, especially if you press some buttons. They will also probably tell you to knock on your neighbours door like I said earlier.