Looking at your logs (
https://www.warcraftlogs.com/reports...mary&source=16), you really want darkmoon deck: promises. Makes your spells cost 2k mana less on average, that's insane value on long fights. 40 spells per minute in 5 minutes = 400k extra mana. Fucking magic. Especially for druids.
Having a retri for wisdom is also really damn good. And you might want to use a mana pot, even the instant 160k mana one is better than nothing if you can't afk 10s for leytorrent.
Looking at your casts (
https://www.warcraftlogs.com/reports...asts&source=16), you should definitely use flourish more than 3 times in 7 minutes. As well as missing out on two tranqs and innervates (that solves a lot of your mana headaches).
Lifebloom uptime is rather low, it's not a big deal, but free regrowths every now and then feel good (also saves mana).
Don't forget to use prolonged power on pull
Most (basically all) of the "how the fuck can they heal so damn much" logs (like
https://www.warcraftlogs.com/ranking...ec=Restoration) follow the same rules: velens, shoulders, 4p t19, darkmoon deck: promises, retri wisdom, innervate on cd (bonus points for moonkin innervate(s), that also gives you haste), using mana pots, definitely going for germination and rejuvenating everyone and everything.
Just look at the analysis of the top maiden mythic log and see how much velens, shoulders and t19 are providing...
https://druid-legendary-analyser.her...H2raz&fight=30
Or more relevant the best Sisters log:
https://druid-legendary-analyser.her...rDVfG8&fight=1. As you can see (
https://www.warcraftlogs.com/reports...ce=4&spell=100), he got 561k mana from wisdom, 240k mana from leytorrent and 409k mana from the darkmoon deck: promises. Literally had more than twice as much mana as yourself. His Wild Growths heal as much as yours, despite not half of them being empowered by 75% from your SotF :P
More mana -> more rejuvs -> more mastery stacks on everyone -> much bigger heals. Once you solve the mana issue, the sky is the limit (woah that sounds edgy).