I have a comment about therapists recommending you not read trauma treatment books, not join trauma therapy groups, etc. Frequently that caution reflects experience and concerns about emotional and psychological stability. Your own stability, and the stability of other participants in a group. For what it is worth, I got the same advice early on and I resented it, but I learned it was good advice and I needed to slow down.
If a workbook is so triggering that you feel you need help with it, then a group setting is likely to make the triggering worse not better. You may not be ready for that particular group, or that group may not be ready for you.
Also, many therapy groups work in progressive stages, building on prior work as they go, so that the participants all start out at roughly the same place and move forward together. DBT groups are that way. New participants usually do not enter the group in the middle; they are required to wait for a new group to start.
Are you a "highly cognitive" person? Do you need, want, tolerate huge amounts of psychoeducation? If so, consider using this group, DID Forum, more heavily. I am highly cognitive and so before I would slow down I needed to know why slowing down would be good for me. Eventually I did learned why and slow down.
As DID expert Richard Kluft is fond of saying, slower is faster because the overall therapy time is reduced if treatment is relatively stable.