Hi Karen,
It took me until strumming was clean before a stiffer pick felt right and stopped rotating in my grip. My thought was it had to do with the direction of the strum, angle of pick, stiffness of the strings, and stiffness of my grip. Persevere through those a bit and you will find strumming just works right and they won’t be a problem. I suggest you use them for at least a few minutes a day before you go back to the floppy one.
One issue with the super soft pick is that you don’t really have good feedback that your technique is off a bit. I even used a 2.0 super stiff “gloss” pick for strumming to help me get the movement cleaned up a bit better once I had the orange working. I can strum with it, but don’t really like to. I used the orange for probably 18 months before starting to really want a slightly stiffer pick and am now using Ultex .73, but this is for a lot of individual string picking along with general use.
I found I didn’t like the nylon. They felt too soft of a connection to the strings. Lots of folks like them, so worth examining to see if they are for you.
The recommendation to get a variety pack (I got two to cover most variations) was a lot of fun to try out and gave the chance to try smaller variations than just 2 picks would. Dunlop has 3 variety packs, and I think the Dunlop LT/MD is a great option to try out some stiffer picks than the nylon. There is also an Acoustic Variety Pack that will better suit the stiffer strings of an acoustic.