Yes, you should use SSDs (and HDDs) for backups.
You should have at least 3 copies of your data. One of them is the master copy, with which you work from your computer. The other two are backups, which should be in 2 different locations, and use two different storage types. The easiest solution would be to use one external HDD and one external SSD. Also, use btrfs (for reasons explained below).