Honestly with the current price of the plasticard any cards I can get my hands on is acceptable, besides thickness is irrelevant unless you can see both sides.
If the card is too thick, just file/sand it down to the right thickness.
As for Yak 3, why not just get an existing model? The cost of the model is about the same as a single packet of card, although some places do offer individual sheets, that might be cheaper.
* * Note * *
1mm is probably too thick for 1/72 scale, 0.4mm or 0.5mm might be more manageable