I found adding fish oil to Denna's meals helped a LOT with low-grade itchies. Our vet was never that excited about her sensitive skin... and she eventually grew out of it... with help...
We switched Denna to a raw diet at about 6 months old. At that age, they're big enough that the 'balance over time' aspect of home-prepared foods really helps. Under 6 months, I'd say you need to provide balanced nutrition daily... above 6 months, if you get everything balanced within one week, you're good.
There's a whole sub-forum here under health about the raw diet.
We started Denna on the "Whole Prey Model" diet, which is easy.... ~30% Bone-in Meat (i.e. whole cut-up chickens or pork ribs), ~60% Boneless Meat, 5% liver and 5% other organs (normally kidney around here). There are a few other "rules", but that's the gist.
Most people prefer to find a good quality kibble that works for their dogs - and there are lots out there.
Many mastiffs have a sensitivity to chicken-based kibble... so you might check for that in what you're feeding. Even using chicken fat as a preservative can cause issues if your pup is sensitive.
I'd recommend:
1. a chicken-free kibble option
2. add 4x a human dose of fish oil capsules to the daily meals (any good cold water fish oil... I'm using NatureMade from Costco) for at least 2-weeks to see if that helps, you can back down to 2x a human dose for maintenance
3. add a good probiotic (human or canine version; I'm using Dogzymes right now, but I rotate through a lot of different versions)
Yogurt does have probiotics, but some dogs can get the itchies from dairy... so unless you KNOW dairy isn't a problem, I might opt to skip the yogurt for now.
Some people swear by coconut oil... it didn't do anything for Denna when we added it to her food, so we stopped doing that.
And... if you're interested in trying a home-prepared raw diet, start doing some research! Search/read here on the forum, and/or ping me if you want some resources.
I love the control of feeding Denna REAL food... and I'm pretty sure she's a fan, too. LOL.