The Grado cartridges are available in two outputs, the 1.5mv that you mention and a 4.5mv version that will work very well with the Slee.
My vote goes to the Audio Technica AT150 and spend the rest on albums. It is an unalloyed value in the market. It has high output and is very arm tolerant, as well as being extremely quiet as far as surface noise goes. You would be able to take it with you when you step up to your next turntable.
My vote goes to the Audio Technica AT150 and spend the rest on albums. It is an unalloyed value in the market. It has high output and is very arm tolerant, as well as being extremely quiet as far as surface noise goes. You would be able to take it with you when you step up to your next turntable.

