I think you are looking for JBOD, or a dynamic spanned volume.
You can tell windows to treat multiple devices as one. That makes space management easier.
But, it is not clear to me what the recovery implications are if one of the volumes fails.
If your two ssd's are equal capacity, then raid-0 might have some benefits.
I did this some time ago without issue. There was no apparent performance advantage though.
Here is an explanation of the recovery implications.
Spanned volumes, unlike striped volumes, do not stripe data across all disks. This means that all data is written to the first logical disk in the span until it is filled, then additional data is written to the next logical disk, and so on.
This means that if a disk in a span fails, only the data that was written to that failed disk is gone. If you lost the first disk in a two-disk span, you'll lose the most data. If you lose the last disk in a span, you'll lose the least amount of data.
Any software capable of reading dynamics disks can get at data on remaining disks in a span, since whole files are stored on it - again, they are not striped across multiple disks. If this were a striped volume, this would not be the case. So, recovery of remaining files is very simple.
Recovery of files that were on the failed disk is a different story and would be the same as recovering data from a failed standalone disk. It depends on the what caused the failure.