I’d recommend trying unflavoured if you’re having any issues with the vanilla, I find the unflavoured to be great.
Totally feel you on the alertness etc, my mood and concentration have really improved, I don’t get the post lunch slump, etc.
As a large person myself, I’d be interested to see how you find your cravings are affected by Huel. I’ve been on it for a month and a half now, porridge in the morning with a banana (which I weigh out, about 500 cals) then 800 cals of Huel to see me through to the evening, and then I can eat something a bit more interesting for dinner. I’m actually finding I crave bad food far less, and am much more able to eat a couple of crisps or a small slice of cake and then stop - which is pretty weird to me. Let me know if you find the same, and good luck!