@nick use what you got "to add a piece of acrylic as a makeshift shelf, but it is flimsier" that is because there are no braces on it. Go to places like TSC or similar in your area and get yourself a few feet of aluminium angle iron. Cut those to length and attach them to the from and back of your acrylic. You'll be surprised how solid it will be. That way you safe what you already have and do not contribute to any more extra stuff. It will also be cheaper than any replacement shelf.