A couple other sealants that are layer-able like Zaino, but will give you better slickness are Blackfire Wet Diamond, Menzerna Powerlock, Wolfgang Deep Gloss Paint Sealant 3.0, and potentially even Chemical Guy's JetSeal109.
I'd highly recommend getting either the Blackfire or Menzerna product - they're very popular and work very well. You'll see we've used them a lot in the threads we've posted in the past.
If you or anyone else need any other product recommendations, please let me know!