Not an expert, but any crank should work. Some specify number of gears for the back, but its slightly silly. I know 10 speed crank works with 8 and 9 speed chain and cassettes. 7 speed chain might not like a 9 and 10 speed crank, so replace chain at same time with an 8 or 9 speed chain (I am fairly certain a 7 speed chain is wider than 9 & 10, it might be same as an 8).

I would replace BB at same time as crank. I would also make sure your crank is tight before buying replacement. They can loosen over time and will look like they lobe in and out as you pedal.