Can a triple stud be replaced with a thinner, stronger material?
There’s four things to consider: 1) structurally support the vertical load from the 3 joists (beam) above, 2) insure there is adequate support under the new post all the way to a footing, 3) adequately support the beam from crushing, 4) provide a support for material wrapping around the post.

we don’t know what the load is on that existing post, but we can assume the triple stud is adequate. Therefore, we can match the strength of the existing post with a new skinny post. I’d use a steel 3”x3” x3/16” wall thickness column, which is MORE than twice as strong as the triple stud post. (I checked for 8’ and 9’ high.) Make sure the steel plates (top and bottom) are bolted into the beam above and floor below with at least 2 - 1/2” bolts.

if the triple stud sat on the subfloor, then there needs to be additional blocking under the post down to the ground.

You’ll need to provide a steel bearing plate at the top and bottom of the steel column that matches the area of the triple stud. Wood compresses easier in side grain than end grain. Therefore, to insure that the beam does not compress, the steel plate must be the same size as the triple stud.

If gypsum board is wrapped around the triple studs, then some wood blocking will need to be added to support the gypsum board.