raised 'beds'

[Sargan]

Bought some 'reusable' grow bags to create 'raised' beds in my greenhouse ..
Marshalls Grow Beds | Four Seasons Greenhouse Gro-System

Now as I creating containers or perhaps simulating a garden raised bed, assume I do not have to fill with 100% gp compost, any suggestions as to what mix of soil / compost would be a good way to go ? , soil I'm using has moderate clay content rather than light sandy consistency.

Thinking that 25% compost might be a good guide - but keen for advice.

Should I also consider adding any grit sand and feed such as 'blood fish & bone' or even Growmore.

Going to be growing veg.

[plantmark]

The RHS recommend a mix of 3 Parts (by volume) Organic Matter, 2 Parts Sharp Sand, 7 Parts Top Soil. I add Pelleted Chicken Manure.