*****
Training with an Instructor is the best way to ensure you are performing the moves safely for you, especially if you have an existing health condition; but below are a few useful videos in the meantime.
Youtube is a great resource, but there are also plenty of poor or inappropriate examples of Tai Chi on there (you don't have to be an expert to post a clip online), so check the feedback before trusting any videos.
*****
BBC's "Trust Me, I'm a Doctor", by Dr Michael Mosley (RIP), said Tai Chi was "as good for you as Zumba":
https://www.bbc.co.uk/programmes/p06nc46v
*****
Mike's 2020 impromptu "lockdown exercise" ; one of our 4 Seasonal Qigongs
www.youtube.com/Mike-Spring-Qigong
*
This is our 'Tree Greets the Day' Qigong also on lockdown
www.youtube.com/Tree-Greets-the-Day
*
and White Tiger's very slightly modified Shibashi 18
www.youtube.com/WTTS_Shibashi_18
*****
Filmed in 1984, here is Prof. Lin Housheng, who arranged the
Shibashi 18 movements/steps/form system in 1979.
www.youtube.com/Master Lin Housheng
*
This is Master Wing Cheung's gentle version of this Shibashi 18
www.youtube.com/Master Wing Cheung
*****
The "Lady in Pink" is well known for the simplified 24 form (the most popular across the world)
Don't let her great flexibility put you off ~ Gao Jiamin is a 32 times gold medal winner
*****
Here is Erle Montaigue's Yang-style Cheng-fu Taijiquan / Tai Chi 108 long form
www.youtube.com/Erle Montaigue
*****
This Sun-style 'Tai Chi for Arthritis' form was created by Dr Paul Lam in 1996:
*
Here is a 50 min talk by Dr Paul Lam on his "Tai Chi for Health Program" clearly a fit 60+ year old in 2009 despite being an Arthritis sufferer from the age of 13.
*****
www.health.harvard.edu/staying-healthy/the-health-benefits-of-tai-chi