How can I install DIY insulation for my walls?

You may be able to do a spray in kind of cellulose insulation into your existing walls and attic. It will require a professional to do the walls but you can rent equipment and materials to do the attic yourself. You can check with local businesses in your area to get estimates.

Here's a article that addresses insulating:

https://budgeting.thenest.com/cheap-ways-insulate-building-23749.html

If you can access your walls from above, you can fill the space between studs with insulation. A couple of other options are as follows:

Basement/crawlspace & attic - add a radiant barrier like Reflectix. It will keep temperatures in that escape through the floor and prevent heat from the roof. Add regular insulation by blowing in the attic as well.

Windows - seal with caulking around windows both inside & out. If not double insulated, add storm windows or replace.

Outlets - add the thin foam insulators to prevent air to penetrate the rooms.

We have just gone through doing all of this in our 1880's built farmhouse and the difference is amazing. We are also going to put new siding on the outside of the house and before we do, we are adding insulation panels to the outside walls.

You may want to consider an energy audit and see where your problem areas are and go from there.

Blown in insulation is not that expensive. They drill holes to put in a pipe and blow the insulation in between the studs. You have to patch and paint the holes where they do so unless you have drop ceilings. They can fill drilling holes under cabinets and blow it in that way and sometimes blow it in from the outside under window sills in the mortar joints by drilling holes and refilling them from the outside.

And . . . Seriously consider having attic fans installed. It is not as expensive as you might imagine. I had some installed when I replaced my roof back in 2005. I have central heat and air as I live in the land of burning inferno in summer. By installing the fans, it cut my energy costs significantly and prolongs the life of your roof as well. Another thing to consider are your windows. One of the leading loss of heat and air. Can be expensive. What I did was research and purchased one side of the house a year. Will take me 4 years to complete. By doing one side at a time, no one will notice the slight difference in models unless one looks really closely. So far they look really good and and improving my out of pocket costs for heat and air.

You could put a hole in the top of the walls and have insulation blown in or add it your self then patch up the walls the blown in kind would be easier.

A few options.... 1? take the drywall off inside and put in R-rated fiberglass batting for your climate, then replace drywall. 2? take off outside home siding and install either fiberglass atting or rigid insulation panels, 3) or drill holes inside or outside and blow-in insulation but its hard to do yourself and get it in there all the way (see videos on YouTube) Home Depot will lend you the equipment if you buy like 20 bags of their blow-in insulation.

Add insulation in the attic, and at the rim joist in the basement.

Check with your local power company for an energy audit, they sometimes have grants for replacing windows, water heaters, appliances etc.

Lots of videos

https://www.google.com/search?q=diy+blown+in+wall+insulation&source=lnms&tbm=vid&sa=X&ved=2ahUKEwjjmqCC88DmAhUKH80KHRZoCRoQ_AUoAnoECAwQBA&biw=1536&bih=740