I usually use a cheap step up converters like this.
They are already pretty small, but I keep wondering if it couldn't be smaller if we replaced the potentiometer with a resistor. And maybe even more components could be removed?
I need it to handle at least 100mA btw, but I'd also be interested in a version that can handle a bit more like 500mA or 1A.
Ones without potentiometer exist. I have some with solder jumpers you can use to set the output to several common voltages. I got them on eBay, but I'm sure you could find them on Aliexpress too with a bit of searching.
But if the PCB has multiple solder jumpers that sounds like wasted space again. Isn't there maybe something like this:
but for 12v output instead of 5v output?
Or maybe we can use the chip that is used on the first converter that I linked and solder it to the Arduino directly? Maybe with a resistor?
Set the pot to the desired voltage level, measure the resistance of the pot, replace the pot with the proper sized resistor, and cut away the unused space of the circuit board.
I like the idea, but I think it's not simple enough.
To give you same background: I'm planning to make one of my projects public and I would like it to be very small, but at the same time very accessible and cheap. I think soldering a few components together is something that even complete beginner could do successfully, but desoldering (especially a 3-pin component) is something I've seen many beginners struggle with.
felic:
I'm planning to make one of my projects public and I would like it to be very small, but at the same time very accessible and cheap.
so you will be getting it inventoried and made in China>
felic:
I think soldering a few components together is something that even complete beginner could do successfully,
You are providing the kit of all parts including the fully tested PCB design?
"I like the idea, but I think it's not simple enough."
So what have you done so far as to building/testing your plan? Have you obtained one of the boards you referenced, removed the components, and put them back on a smaller custom/DIY board?
Just curious, why do you need 12V? If you can power whatever the mystery component is with 5V, then you wouldn't need the boost converter.
12v at 500mA is a lot of watts for the size of converter you’ve shown...
felic:
I like the idea, but I think it's not simple enough.
To give you same background: I'm planning to make one of my projects public and I would like it to be very small, but at the same time very accessible and cheap. I think soldering a few components together is something that even complete beginner could do successfully, but desoldering (especially a 3-pin component) is something I've seen many beginners struggle with.
How simple do you want it?
One or two components?
Why would they want to de-solder?
Please explain your project, what is its application?
If you want our advice, we need as much info as possible.
Thanks.. Tom.. 
"felic" seems to be suffering the Sinatra Syndrome and lying low. 
What’s the source of 5V? Boost converters are not as efficient as bucks.
