One thing about Vit c is that it can be hard on the stomach. Lozenges or drops that partly go through the buccal mucosa directly into the bloodstream might help with that and also likely would lower the needed dose as the stomach absorbs some of it.
That's interesting. Do you know any good brands of this type of C?
Right, B vitamins.
To get them working you need
magnesium
molybdenum
phosphate
biotin
cysteine
folate
selenium
zinc
copper
Eggs are an all-round super food which will give you nearly all of these.
You're taking magnesium anyway, but to boost it you can snack on almonds and cashews. You'll also get it in figs and parsnips.
For molybdenum, another v important one, you really do need to eat beans, lentils etc. of all kinds. If the farting becomes simply too much for you (or your wife?) you can try oysters! I have to admit that Mr. Athene registered too many complaints in this department, so I have started taking a molybdenum supplement instead.
Biotin is made by the good baceria in the gut and if your immune system is substandard, then you won't have enough of those. You can either take a lot of probiotics or a biotin supplement. Biotin is essential for energy production too. If you have a real deficiency your hair starts thinning and you can even get bald patches.
The other biggie is zinc. You'll get that in beef, eggs, liver, milk, herrings, ginger, lamb, sunflower and pumpkin seeds, and seafood.
Most of the others are trace minerals so you should get them in nearly all veg, provided they were grown in nutrient rich soil (rather than greenhouses with artificial fertilisers!)
Some foods that are super nutrient rich are avocados, apricots, nuts of all kinds, and cantalupe melons.
It's a good idea to have a choice of nutricious salty snacks around to give you a boost when your energy flags. I have olives and parma ham a lot, salted nuts, and for you bits of cheese would probably be good too. (Ah I miss cheese! I used to be like Wallace and Gromit, a cheese worshipper!)
I hope that's given you some good ideas!