You don't need a second SSD.
The boot drive does not have to be part of your RAID disk.
Why do you need raid 10?
Have you considered running two disks in your PC as raid 0 (stripe) and another one 2TB+ disk to put in an external USB enclosure (or NAS box) to be used as a backup for your main disk.
The advantage is that you can keep your backup in another room or offsite.
The disadvantage is that you have to remember to do your backups.
Remember that RAID is no substitute for backup.
Also stay away from RAID 5