What is the simplest way to export (from raw, then enhanced) photoshop images in the original resolution as JPGs, rather than giving a specific size?
By default, File > Save for Web will save the image at the same dimensions and resolution as the original. There is a quality setting you can lower to get more compression, so a smaller file size in KB or MB, but the resolution and dimensions will stay the same as the original.
At the bottom of the dialog there are image size settings which you can use if you want to resize the image, but by default it's 100%.
File > Save As will do the same thing as Save for Web, there is just a bit less fine control over the quality options.
If you want lossless compression (no loss in quality) then you could try TIFF or JPEG2000 from the File > Save As menu.