Using an ATTINY85 to program an ATMEGA128? Or bypass for USB access.

I wish to add serial in/out via USB to my custom arduino.
So I currently have 3 options as far as I can tell.

1: Use a serial to mini-usb breakout adapter I have. Of course this is the most direct solution. But the circuit board doesn't have any sort of mounting holes, and I really don't want to use glue and tie strips to mount a board I am going to use force to use the usb port of a dozen times a day.
It's also rather large and doesn't fit on my device in any neat and natural way.

2: Use a ATTINY ready on a board from digispark I also have.
Can I use this board to program my bot, or perhaps bypass the ATTINY and use the USB port and serial handling circuitry for my custom arduino directly?
This board would fit perfectly if this is possible.

3: Try to find another module and wait another month or 2 for shipping.
If you think this is the best option, do you have any suggestion for small serial modules with attachment points? I have been searching for replacements, but I haven't found the best options so far.

My device is built on a solderable breadboard, so I can also build my serial circuitry myself if you believe this is doable.

I really like these: 1PCS CH340E USB to TTL Serial Converter, 5V/3.3V Model:BTE17 06 Alternative CH340G Module| | - AliExpress

I haven't done extensive testing, and they seem a little too good to be true, but I've put them in a couple of projects that seem to work fine...


Looks perfect! So you just hook it up and it works by itself?
What sort of housing is that you're using for them?

It's a shame Aliexpress uses around 2 months to ship here. I guess I'll just hook up the other serial expansion board and let it float while I wait.