The one
@WickedFog showed in the photo has a dial down at the base of the handle. You could also use an external rheostat like the one I posted in your other thread with the 100W iron. I use that for both my 60W and 100W. My cheap 60W has a little dial on it, but I set it to max, then wrapped tape around it and rely on the external one.
The solder I have is old kester Sn60Pb40 "44" rosin core .031" diameter 1lb roll I got from work 20 years ago. We used to replace chips on circuit boards for scanner guns and I worked on old credit card embossing machines (that were the size of a lay down freezer and weight 500lbs). Have had the same roll for years and I know what you mean about needing 2 feet of it to just solder an XT90! I hand my wife the end of the wire and the spool, then I back up 15 feet or so, put the wire in a drill, then spin it as I slowly walk towards her. Then I end up with 13-14 feet of 2 wire braid that I wrap up in a spool. That usually gets me by for a few months.
This stuff worked great for soldering the lipo tabs when I was building 4S and 6S packs out of old packs I had:
https://www.amazon.com/gp/product/B010UMSB9Y
Ruined my 100W iron tip though... so I bought a new one for it to use for regular solder and kept the old one for the aluminum stuff. I know it's bad to do, but after I cleaned all the black off of it the aluminum flux stuff left all over it with sandpaper, it still soldered the aluminum stuff just fine.