I agree that the way you're currently using skills wouldn't help much with talking in therapy. They seem to be about taking you away from distress, rather than keeping you present without getting too distressed in the first place.
All these things help on some level and I do use them, but I can't see how they're going to help me to talk about stuff, because all of them really kind of focus on stopping the stuff in my head don't they? And what I feel (I think) is that if I'm going to be able to talk about then actually I need to be able to stay with it.
Grounding is actually about staying with it. How I think it would apply to your therapy situation is not the reactive type of grounding where you bring yourself back to the present when things go badly, but a regular practice to create a more constant, secure connection to the earth and your surroundings. The aim is to make your base point more secure so it's easier to stay there or return there quickly when under extra stress. Which means frequently practising grounding exercises throughout each day, for example feeling the ground as you walk, orientating yourself to where north is and which direction your home is in, imagining something running through you and down into the earth etc.
I'm a very visual person so some of the things I use are based on visualising things, so actually pushing things out of the way in my head, or squashing them down, this is especially useful when my head is flooding with too many things (my head very rarely stays in one place for long and often feels like it is in several places at the same time).
Again, what you're talking about here seems to be about dealing with a reaction that's already happening. Which is important as an emergency measure, but for talking in therapy you need a different sort of safety. It's about building the ability to stay feeling safe as you go along, not just about reacting when you're already feeling unsafe.
I think visualisation is the single most effective tool for building the second kind of safety. If you can visualise easily, then you have a huge advantage. What's important is what you visualise and how. That's also very individual so if I told you what works for me then it might be something that wouldn't work for you at all. Also, I might suggest something based on what you said that would be right off the mark. Bearing that in mind, I'm going to give an example of the sort of thing but it might not be
your sort of thing at all, it's only to give an idea.
To take one thing you said, I might come up with an image of someone managing my thoughts while I talk, containing them by keeping them all in a box and taking out only the one I need at the time. I would imagine a very powerful, calm and capable figure (the Manager of Thoughts) surrounded by many swirling slips of paper which each had a thought written on them. I'd imagine what the thoughts were, ie what was written on the slips of paper. Not in too much detail if that would be upsetting - it could be generalised things like "What happened when I was 12" or general fears and feelings like "Overwhelm", "Too much". Or it could be specific things I tend to think.
I would imagine the Manager of Thoughts taking hold of them and putting them into a strong box with a lid until they were all in there and the air was calm and clear. I notice him doing this and see the thoughts (what's written on the papers) disappear into the box one by one. I notice how safe and calm everything is now. Then the Manager of Thoughts takes out one single thought and firmly replaces the lid on the others. He smiles and hands me the thought, and I read it. It says one short sentence that I would like to say to my therapist. I notice that more slips of paper/thoughts are now starting to swirl in the air, but the moment they appear the Manager of Thoughts takes hold of them, puts them firmly into the box and shuts the lid tight. The air is calm and clear again. I feel very peaceful. I know the Manager of Thoughts is in control and looking after me. I no longer need to watch him as he does this. He smiles and looks at the paper I'm holding. I calmly read what it says...
And so on, up to saying it out aloud and feeling calm and safe.
I would do this visualisation many times a day, every day, always focussing on what I wanted to say to my therapist. I would do it when nothing in particular was going on with me, I would do it when I did feel crowded by too many thoughts and I would do it whenever I thought about my next therapy session. I would do it very particularly before the session and connect to it when I sat down and began the session.
Like I say, an image that would work for you might be completely different. You probably need more than one visualisation (I used to use five different visualisations, initially). But even one should make some sort of difference. My experience was that doing something consistently (every day, several times a day) was more important than feeling I was doing it brilliantly. The effect was small at first but as I continued it got much stronger until it was very powerful.
Even if this isn't a good example for you, I hope that gives some idea of how you could use the skills towards talking in therapy?