External SSD enclosures, need advice

My boss has an external SSD enclosure, probably purchased as an end-user solution and probably using a 1.8" drive because it is so small. It runs off the single USB plug that connects it to his PC.

I like the idea of moving away from a bunch of 16 and 32GB USB sticks to one external SSD that fits in my pocket, but I'd rather assemble it myself if I can get the parts cheaper. Here are my challenges:

1.8" would be preferable, but there seems to be little available in terms of SSD standalone drives or SSD enclosures for this size. They would probably be more expensive anyway since they are not common.

2.5" enclosures would probably be ok, as long as it is as small as possible. I have a 2.5" SSD in my desktop, and something that is just slightly larger would be ok.

However, a lot of the 2.5" enclosures use dual USB to power the drive. Do SSDs really require that extra power, or is that an indication that the case is designed for a disk-based HD? I'd strongly prefer a solution that used data and power from one USB cable, no dual USB or external power needed.

Also, is there any height difference between 2.5" SSDs and disk HDs? I'd rather get a snug fit and not have to worry about an SSD rattling around in the enclosure.

I'm ok with USB2.0 because that's all I have at home and work; I'm just thinking I can get a lot more storage in a mobile solid state package rather than buying a bunch of flash drives (I have run out of USB slots at work because I have 3 different thumb drives plugged in). I know I'm not getting the speed, I'm just looking for small, portable, and large capacity vs a handful of USB sticks.

Thanks for any input/advice,
Keith