Literary speaking, there is a very little difference between the terms selfish self-interest and selfless Self-interest (apart from the subject each pertains to). Any action or thing that gives comfort to the body but ignores the soul can be regarded as selfish self-interest. 

We are essentially the soul. The body is nothing but our (i.e. the soul’s) vehicle or instrument. Therefore, it would be indeed a great stupidity to do something which does good to the vehicle or the instrument at the cost of its owner! On the contrary, the prime focus of the selfless Self-interest would always be on the welfare of the soul. When the welfare of the soul is taken care of, it would automatically create all necessary situations that makes the body feel happy and gratified. Only thing that gets restrained is any unnecessary self-indulgence. 

Whenever we happen to come across a situation wherein we may have to give some trouble to the body for the sake of doing good to the soul, we must do so without any hesitation which would be the only prudent option. This is exactly what is known as selfless Self-interest (parmaartha) which means the supreme (parama) Self-interest (swaartha). 
 

-Pt. Shriram Sharma Acharya

Translated from - Pandit Shriram Sharma Acharya’s work

Yug Nirmaan Yojanaa: Darshan, swaroop va kaaryakram 66:2.68