My SG1 doesn’t handle thick cardstock well. I have some index cards that are thicker than normal index cards and they are the thickest I can feed. Greeting cards or the nice letterhead cardstock my wife got me, do not fit.
If this is the case, I worry that there may be something poorly adjusted on your machine.
These standards were designed for offices using thicker carbon packs of 10 or more sheets of paper for carbon copies at the same time. I can easily roll a stack of 13 standard Oxford index cards (approximately a tenth of an inch!) into my SG1 at the same time. It's only when I go over this that problems begin.
I just tried it as an experiment, but if I'm careful, I can put a piece of corrugated cardboard from a standard Amazon box into my SG1 and type on it. (Hint for those considering it: the corrugation doesn't give the best results from an imprint standpoint. The machine is also going to compress the cardboard and put "wrinkles" into the corrugation as it winds through the platen.)
If the bigger standards aren't going to handle the thickness of card stock you're attempting to type on the portables and ultraportables are going to be even worse.