MarketPress: How to show customer how much weight he can add before paying more shipping

We ship from Peru worldwide. The shipping costs are weight and region related. As an example (to the US): From 250g on: 21 USD, From 500g on: 32 USD, from 1kg on: 53 USD.

There are articles which are very light (like necklaces under 100g), and other ones around 400-900g (weavings).

To make the best out of the high postage means being as close as possible to next weight interval.

(1) How can I show to a customer the difference of weight left to the next weight interval?

(2) How can I show recommendations of products fitting into the weight difference between the total weight of products in his cart and the next weight interval?

Example:

Customer has a weaving in the cart (700g).

I want to show a message like “for the same shipping cost you could add….” and then it shows a list of products all weighing less than 300g (because the next weight interval with 21 USD more of shipping costs starts with 1kg).

Thank you for any hints!!!