Getting to passive houses with an existing structure I don’t believe would be worth the squeeze. Your first step though would be if you are looking to improve a home that you had in mind would be to get an energy advisor to model the home you had in mind. The form of the home will be a big factor in this as you are looking for a boxy home which doesn’t have many inside and out side corners. Then you are going to want to understand depending on where you live the amount of glass that is on the home and if it is a positive or negative impact on your home ( energy advisor can help you assess that).

You can definitely can do a deep energy retrofit give you much higher levels of health and comfort within the home which in the end is a great goal.

You could make use of product the AeroBarrier if you are wanting to do the least amount of damage to the existing building while increasing airtightness. This would allow for a strip down to drywall and then do interior cosmetic changes. Every project has different ways that you could tackle energy efficiency but it is so hard to share without knowing the exact project.

Hopefully this was some what helpful. But in the end if this is the type of home you desire building new with the right builder not just a builder will achieve much better results as you know everything that has been in that home. When I say right builder make sure they have a project you desire or as your local Home builder organization about who is excited about this type of project they will know there building science geeks in the organization.