Cranks don't care how many "speeds" you have in back so any road or MTB crank will work. A newer 9-speed or 10-speed crank may not be happy with your wider chain but otherwise, they will work. If you do change the crank, you will most likely need a new bottom bracket to match.

As best I can see from the photos, you have a crank with a 110 mm BCD (bolt circle diameter) so any chainring with that bolt circle will work. You can fit as small as a 33T chainring to that crank so you can regear it as you wish and chainrings in that bolt circle diameter are quite available.