I own several external 2.5'' HDDs on the 1 TB range where I save my data. Samsung has worked well for me, but now I need more space.

One option would be to buy an external SSD instead of HDD.

Another would be to get an external NVME, but so far I haven't found cases for them.

Nowadays we even have 1 TB flash drives, should I get one of these instead?

I could also buy 2 0.5 TB micro SD cards instead.

So many options make it difficult to decide.

What brands and technologies do you recommend?

Software is going to be debian based.