I used to have a product called n-large. https://www.amazon.co.uk/Prolab-Larg.../dp/B000OUAJ2A
They don't make this anymore though.
I moved it with water, it was thin, didn't upset my stomach, digested fast, I grew like a weed on it twice a day and the flavour was mild so I could drink it easily.
The best thing was I could make it in the morning, pour into a bottle, drink it through the day without it 'setting' or 'thickening' or changing texture, which was perfect for me.

i have tried various other powders, none of which work for me.

1. Reflex Mass Gainer Xtreme: very thick despite adding lots of water (2 massive scoops), and the taste it not great.
2. Optimum Serious mass gainer: way too thick its almost like eating a meal and tbh I started to look watery and bloated on this.
3. BulkPowder/MyProtein mass gainer; cheap but taste is not great and didn't really see any gains on this.
4. Mutant Mass: Was okay, lots of gas though so stopped this.
5. USN muscle fuel anabolic: this was closer to n-large, bit sweet, but I can go for this if there is nothing else.

Any further recommendations are welcome!