Multiple disk groups is definitely a good idea for a variety of reasons.
To add another disk group, it's simple enough, see the official guide here: Create a Disk Group on a vSAN Host
Selecting the cluster > Configure > Disk Management will show you current disk groups setup in vSAN
Add another buffer(AF)/cache(hybrid) device together with 1 or more capacity devices and create nother diskgroup.
Apart from having 2 DGs or more, you may also want to consider having several VMDKs per SQL server to spread out your DBs. Adding additional DGs can linearly increase performance, but you should take into account whether you will be utilizing dedupe and compression in the cluster. Since we currently do Dedupe and Compression at the DG level, having bigger DGs will yield better dedupe ratio, while having more DGs may yield better performance. It's a design decision you will need to make based on your requirements.