Combining warlock or sorcerer with cleric is a bit difficult since clerics need high wisdom for their spells to succeed, while the other two need high charisma.
The first two combinations that come to my mind would be tempest cleric + storm sorcerer (sorcerer 1 -> cleric 2 -> sorcerer 10) or war cleric + pact of the blade warlock (cleric 1 -> warlock 5 -> cleric 7). But those don't really fit to Selune as goddess.
You could try light cleric + gold draconic sorcerer to get a fire mage with some healing and support spells. It's not the most optimal multiclass combination, but it should be strong enough to have fun and complete the game. For the leveling order I'd start with sorcerer 1 followed by cleric 1. Then bring one of the classes to 5 to get access to 3rd level spells and finish however you like. I'd probably go for cleric 5 + sorcerer 7 but you could also do it the other way round.
