I had to use an iPhone 3GS and a Samsung S2 whilst my iPhone 5S got repaired.
I had an adapter to go from nano to micro sim. I also had a "normal" (not credit card) sized sim that had a laser-cut pop-out micro-sim in it.
I put the nano-micro adapter inside the micro-mini sim. Worked okay for me.
Edited to add pics.
Left to right:
Mini, Micro, Micro-nano adapter, nano.
Second pic, nano in micro-nano adapter in mini