Use of less and lesser vs lesser and lesser

The consumer on an indifference curve is willing to sacrifice less and lesser of good y to get an additional unit of good x.

This is an answer I got from a model answer paper while preparing for economics exam..my question is...is the use of "less and lesser" here, grammatically correct?

No. It is not correct.

The consumer on an indifference curve is willing to sacrifice less and less of commodity y to get an additional unit of commodity x.

is a better sentence in my opinion

There are no such expressions as less and lesser or lesser and lesser

The correct expression is less and less.

Also first time I have ever seen goods in singular. However it does exist in economics it seems. Note that the word good is not used in the description except once:

In economics, a good is a material that satisfies human wants and provides utility, for example, to a consumer making a purchase. A common distinction is made between 'goods' that are tangible property (also called goods) and services, which are non-physical. Commodities may be used as a synonym for economic goods but often refer to marketable raw materials and primary products.

Lastly (before your edit) I would expect on an indifference curve