Tai chi IS meditation. One reason for practising meditation in a chair or otherwise is to discover what it feels like to feel good. Once you discover the feeling, you do the form in the same way and continue to feel good.
Once you know what it feels like to feel good and how to be the feeling, you don't need to meditate in any particular way. You just do what feels good and don't do what doesn't feel good - remembering that thinking is also doing.
There is a trap if you get the idea that the meditation, or whatever, is ultimately causing the feeling. You are causing the feeling and you are chosing to experience this feeling while sitting in a chair or doing the form or washing the dishes.
I used to meditate as an escape from reality (just like I used to do many other things). And, it can be an escape - 20 minutes out of body or off to the planet Koos Bar. But when I came back I was still the same me, and I was still carrying the same burden. I had only managed to escape it for a time.
It was only when I stopped 'meditating' that I realised I had not been really meditating at all. I was caught up in the illusion of cause and effect.
This is only a suggestion: stop and ask yourself, "Do I feel good?" a few times and actually feel before you answer. Next, once you feel good, and you will, ask yourself, "Can I keep feeling good?" Then ask, "Do I want to keep feeling good?" THEN, do the form. This is not a 'way' or a method, it is just one of the many things you can do to feel good. And since it has always felt better (to me) to feel good before starting the form than to do the form in the hope that it will make me feel good (and it will), this is what I prefer.
If you are not feeling good while doing the form, stop and do something that does feel good, like sitting in a chair.
R. M. Field