Adding a link with quantity button prodcut and add to cart button

Hi
Im needing advise on the best way to add 1 related product to the product page below the short description and the add to cart button of a product page, i need it to looked like the grouped product display with a quantity box, product named linked and add to cart button.
What is the best way to achieve this
a form, (which i have tried and struggled with)
hooks (ive never done before)
shortcodes (which i havent used before)
Is there a plugin that can do this.

All advise is much apprecaited