A full aperture, astronomy industry approved solar filter is the only filter I would trust with my precious eyesight.
I have purchased sheets of
Baader AstroSolar Safety Film for Visual use and Photographic use and made my own full aperture solar filters. Full aperture means that it sits in front of the objective thus blocking the harmful radiation before it reaches the main mirror or lens.
Personally, I would only purchase from a dealer that I trusted and who had a good reputation within the astronomy community.
I’ve gone a bit over the top in my reply as from your post, you certainly seem to understand the issues and be familiar with the dangers, but I thought it worthwhile just in case a beginner stumbles in here one day.
Cheers
Dennis