What is your advice to store pictures on the long term ?

I am not a photographer and I don't know anything on the topic. I have a lot of pictures that I want to store safely for as long as possible.

Do you have tips, do's and don't ?

What format would you use ? Currently I have a mix of a lot of different formats, but I can't use the heavier ones. For example I have some TIFF, CR2, PNG, etc. which are pretty heavy, and I'd like to convert them in a lighter format. I'd be okay losing some quality if there's no choice, but not too much if possible !

How important is it to use lossless formats ? Is JPEG-2000 a good idea ?

Thanks a lot for your help, have a nice day !