404 and .htaccess

Hi
I have a redirect question.
This morning my site was all 100% ok. I recently moved the site to WP and of course I have old HTML pages that are left over from the site. These pages have good rankings in SE so I dont want to lose the trafic from them.
I created an .htaccess file with the following format
redirect permanent /wealth_and_success_video_1.htm https://totusunus.com/index.php
This worked fine. Later on I went the site and EVERY WP page other than the home pages gave a 404 page could not be found message. Disaster!
I deleted the .htaccess but still no go, still 404.

I then found help on a past forum post for this problem.
It had to do with permalinks.
To resolve the 404 for all pages I went to permalinks, deleted the custom setting there which was /%category%/%postname%/ and then checked another option and then updated. I then opened up permalinks again and then selected custom and RE pasted in the original /%category%/%postname%/ then updated this Voila! all OK…

So… how can I use .htaccess or any other method to redirect from my old html pages to the new WP site without screwing up the permalinks (if this is what it did)

Many Thanks