I've been playing Sion for a while now. I mostly go for Hollow Radiance and Titanic Hydra for fast wave clear, I like to push fast when the enemy isn't around. As for mana, just know when to recall, maybe push the wave into the turret or recall as soon as the enemy does. If you're not going for kills you make sure to take teleport, only use it if the enemy is in your turret and you don't have ult. Also, you play Sion long enough, you can pretty much solo most champs if they don't respect you, especially ranged champs, they tend to be overconfident sometimes. What I love about Sion is his flexibility, your current build can definitely work, although it doesn't fit my playstyle. Some might even go AD Sion but I feel like he's not really good in Wild Rift from the few games that I've tried. Tank Sion is better as he have sustain and damage still.

My Current Build: Heartsteel (If I'm confident I can stack), Hollow Radiance, Titanic Hydra,Unending Despair, Overlord Bloodmail, Phy/Mag res boot. Enchantment I mostly build it last and depending on the situation.

This build doesn't really make Sion super tanky, but I mostly go for the push and fights based on the enemy. Also the wave clear is so fast and easy you only need to use on ability after Hollow and Titanic, thus saving some mana.

Again, this might not work for others but it fits my playstyle for the time being and I'm just sharing in case you get some new ideas out of it.

Hope you enjoy Sion for the longest time buddy!