"Bulky parcel"  goes up to 120 x 80 x 80 cm, and up to 30kg.    That availability depends on category so you need to change category or sub-category until it's an option.  

Or you could use "Oversized" to opt out of Simple Delivery and buy your own postage.    That also depends on category.    If you select it click on Add Primary Service and enter postage cost.     It has to be done on a laptop or desktop rather than the app.