SMS and Signal is all I use as well. I have never used WhatsApp and I do not know if any of my friends who do.
You mention 50% of your friends use iPhone and the cross platform use of Signal and Signal’s features may be a way to get more friends to use Signal. This does not really work for myself but I have friends that Video Chat predominately.
I ask here not for myself, but to answer this common question. Is there a more secure way to use WhatsApp, than using a work profile.
What could you do with no expense and usability not being an issue?
Isolated hardware, private network only used for WhatsApp, software solutions…