For future reference, it is a great option to purchase mounts and pets as a long-term investment. Not only do their prices scale well even when a new expansion drops, but there is always a demand for them. The only drawback to this strategy is you would need a hefty amount of initial wow gold investment and also maybe have to go through the motions of spending for a guild bank.
If you prospect your own Ores, usually you will get a lot of [Lesser Moonstone] too, but even if you don't prospect the Ores, sometimes 2 Lesser Moonstone is cheaper than one Moss Agate. So get the recipe [Design: Amulet of the Moon] and use up all your Lesser Moonstone. This recipe turns yellow at 140, you might need to make more than 30 of these.
Congratulations on reaching Level 120! There are a myriad of new things to do. The first thing you should do is head to your faction hub ship where you have been doing your mission table quests and footholds to pick up and complete the quests necessary to unlock World Quests. World Quests will provide you an opportunity to grind reputation levels, acquire gear, and gather Azerite. There are tons of new things to do that we will cover in our Level 120 Battle Guide found here: Level 120 Battle Guide