Merging meshes

Hi Everyone, i'm trying to merge meshes with different material on a single mesh with different submeshes associated: every mesh i try to merge is considered as a single submesh of the new generated gameobject, each with the original material. Here my code:

     public void Merge(GameObject[] gameObjects, string Name)
     {
         if (gameObjects.Length == 0) return;

         Material[] materials;
         MeshFilter[] meshFilters = new MeshFilter[gameObjects.Length];
         MeshRenderer[] meshRenderers = new MeshRenderer[gameObjects.Length];
         Mesh combinedMesh = new Mesh();
         combinedMesh.subMeshCount = gameObjects.Length;
         int size = 0;

         for (int i = 0; i < gameObjects.Length; i++)
         {
             meshFilters[i] = gameObjects[i].GetComponent<MeshFilter>();
             meshRenderers[i] = gameObjects[i].GetComponent<MeshRenderer>();
             size = meshRenderers[i].sharedMaterials.Length + size;
         }

         materials = new Material[size];
         CombineInstance[] combine = new CombineInstance[gameObjects.Length];
        
         for (int i = 0; i < gameObjects.Length; i++)
         {
             int j;

             if (i == 0)
             {
                 j = 0;
             }
             else
             {
                 j = meshRenderers[i - 1].sharedMaterials.Length;
             }

             combine[i].subMeshIndex = i;
             combine[i].mesh = meshFilters[i].sharedMesh;                
             combine[i].transform = meshFilters[i].transform.localToWorldMatrix;

             for (int k = 0; k < meshRenderers[i].sharedMaterials.Length; k++)
             {
                 materials[j + k] = meshRenderers[i].sharedMaterials[k];
             }
            
         }
         

         combinedMesh.CombineMeshes(combine);

         AssetDatabase.CreateAsset(combinedMesh, "Assets/" + Name + ".asset");

         GameObject combinedObject = new GameObject(Name);
         var filter = combinedObject.AddComponent<MeshFilter>();
         filter.sharedMesh = combinedMesh;
         var renderer = combinedObject.AddComponent<MeshRenderer>();
         renderer.sharedMaterials = materials;
     }
     #endregion

unfortunately i'm not able to have the final gameobject with all the preexisting materials of each mesh to merge: could someone help me in this? Thanks a lot,