So many possibilities, pastel makes almost everything look cleaner/brighter. Typical good looking combos would be a lesser pastel or bumblebee, but my favorite two gene combo with pastel lately is pastel ghi.
Re: What morph would be good to breed with if since I have a pastel female ball pytho
personally i'd go lesser/butter for the first pairing. lesser/butter pastels are so nice and clean and you'd then have a 2 enhancer gene morph. Bring a spider into the mix with a lesser pastel and you've got the potential for a queen bee.
Personally I'd go for more color in your hatchlings if you were to start with just Pastel. A nice target would be an Orange Dream Fire Bumble bee. (Orange Dream + Fire + Pastel + Spider). Super cool snake with a cool pattern and lots of color! You could get a male with any of these genes and hold back babies, get a different male down the road with more genes and breed back into your offspring, etc...