How to migrate to an SSD without losing dual boot?

As long as the SSD is larger you can clone it as @Wollie mentioned. Then once you have the new drive working you can expand your existing partitions or create a new partition to use the additional space on the drive so space doesn’t go to waste.

Here is a link to a video that pretty much walks you through step by step how to do it. (including everything you would need.

For his example he is using ubuntu usb boot to do the cloning however you could easily use the manjaro usb boot disk and the commands would be exactly the same). The video even goes over what you have to do if your windows partition is encrypted.