Custom block shape

I am trying to make a decoration block called a golden cow. it is a more complex shape and i have two issues. #1: Its hitbox is still a block, and there isn't really a preset that will fit the entity shape well, and I don't know how to make its hitbox the same shape as the block. (I'm using blockbench to make the custom model). #2 The texture i exported is the kind that shows every side and it almost kind of folds (if you know what i mean) I don't have textures for each individual side. Whenever I put the shape as the model it only lets me put one texture on it (the base/bottom slot), and I tried putting the texture on it, but it ended up looking like the right shape, but with a block-shaped hitbox and the null texture (including the bottom), strangely, the breaking particles were of the texture I wanted. Does anyone have any way to fix this?