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Based on the single stage design, only with more transistors because I'm a masochist.
Upper pot is negative input, lower pot is positive. Flip the switch to change from DC input to AC input. Negative feedback is set up to give a gain of 2.
This time instead of one differential amplifier, this op amp contains two diff amp stages to further increase gain, more robust current mirrors for more accurate current sourcing and sinking, and a CMOS output buffer to negate the output and provide low impedance at the output. MOSFETs are a great choice to build op amps from, since they provide high impedence input, low impedence output, and a large frequency response. It is important to note that the nMOS and pMOS transistors should be well-matched complimentary pairs. There are a few good online resources that provide part numbers for decent complimentary pairs with near equivalent characteristics:
https://electronics.stackexchange.com/questions/108388/is-there-a-popular-small-signal-pfet-equivalent-to-nfets-2n7000-or-bs170
https://www.newark.com/c/semiconductors-discretes/fets/dual-mosfets?transistor-polarity=complementary-np-channel
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