OK, 70 to 90 grams sounds like a lot of weight. I tried several smaller weights, the highest being 37 grams (stayed with that one). Maybe, I should have gone a bit higher. At the time I tried it, all hardware stores in Germany where closed due to the pandemic and I did not have appropriate washers. So I ended up using old coins from my travels (Costa Rican coins worked best because they are quite heavy 
).
It is not a problem at all to use switches instead of the add-on board for the controls. I also did it in my boombox.
I used a pushbutton rocker switch for Play/Pause and Next. Would have used more switches but there was not enough space. The thing that is important here is to use switches of pushbutton-style. What the Arylic board expects is just a short impulse of a certain voltage, not a constant voltage level.
You can look up the correct value of the resistor (R60…70) you have to connect to the switch to control a specific functionality.
One important remark: You must not install resistor R47 (the one marked in red in the schematic) since this resistor is already installed on the board. This is an error in the schematic that led several people (including me) wonder why the values of R60…70 printed in the schematic did not work
. They did not work if you added your “own” R47 because this shifted the voltage levels. Although this error is known now it might still be a good idea to put together your control circuit on a breadboard first.
Regards, Sven