retrocomputing

What about the C64? It had both 5.25 (model 1541) and 3.5" (model 1581) drives.

Commodore 1581

It could be used with Commodore 128, which could run CP/M.

Does Famicom Disk System count?

Some higher-end MSX machines had 3.5" drives as an option.

Commodore released the 1581 floppy drive in 1987, which was for their 8-bit systems. The Apple iiGS had one as well (though it would also work on Macs of the time, as well as the other Apple ii computers as long as they had a floppy drive port (sometimes this meant needing a controller card)).

3.5” disks were standard on the Acorn Electron, and optional upgrades for the BBC Micro and BBC Master.

Thanks so far - all of these are really good - As I said I already have an apple IIC+ so that covers the 6502 side of things I think. I am thinking of something like a Vixen, or Ortrona only with the 3.5" drives- All in one. Or something I could build myself with like 2 of these drives. In that case, I can use my laptop as its screen and keyboard through a USB/Serial adapter. But an SX64 shape is what I am looking for.

You could get 3.5" drives for the Amstrads CPC and PCW cos the 3" disks were basically impossible to get.

VTech Laser 128.

But that's just an Apple II clone.