"consisting mostly of" is correct and useable in written English.
It is used to describe what something is composed of. For example: The garden consists mostly of roses and tulips.
Constanţa judeţ, consisting mostly of lowlands, contains several lakes.
All members are men, but there's a women's auxiliary consisting mostly of members' wivews.
Socit Gnrale's business here is also limited, consisting mostly of setting up transfers and repatriating funds.
Eric Idle had prepared something consisting mostly of the old standards.
We had a large and attentive audience, consisting mostly of fans of Reg, I suspect.
In Berlin, German leaders unveiled a 480 billion package consisting mostly of loan guarantees.
He began with an hourlong set consisting mostly of curios and cuts from other albums.
Cinematically, "Outfoxed" is a straightforward film, consisting mostly of clips and talking heads.
Consisting mostly of women, it has become famous for its inter-tribal composition and multilingual performances.
It is filed in a group consisting mostly of complaints from private drivers.
Male guides wearing industrial uniforms took visitors around exhibits consisting mostly of wall panels.
