Let me present a small table-top mangle:
It is not exactly portable, as the stand and mechanism are cast iron. OTOH, it stays put :)
To change the pressure, there is a spring under the front "table" (that is easily lifted out):
There is a protector sheet fastened to the top roller:
This sheet should preferrably be longer, but I haven't bothered to change it. Shopping for a "mangle sheet" in Sweden will get you a piece of tightly woven (plain weave) unbleached linen.
To use it, put the (in this case) towel as near to where the protector sheet is fastened as possible, the hem as parallell to the roller as possible, and lower the "clutch" bar. The bar is both what engages the gears and also to protect your fingers. Start cranking, just to make sure the towel is in place, and held.
As you go on cranking, make sure the towel stays flat (always smooth it towards the sides). When it has gone a three-quarter turn, the hem is visible through the protector.
The "bump" of the hem will show on the towel - the only way to avoid that is to let the towel go straight through - like I did with this shawl:
Once the towel has all gone onto the roller, you crank away "until done" - then disengage the clutch bar, and drag the mangled piece towards you. The top roller spins free when the bar is in the up position.
For best result, the goods should be slightly moist. If it is dry, sprinkle with water and let it sit for some hours in a plastic bag, to let the moisture even out.