How can I make a garage more comfortable ?

Insulating the garage is going to be your best solution. You might want to take out the large garage door and replace it with a wall with windows for more light while you are it it.

Hi. First check with your city/county (etc.) on what you can/cannot do along with your homeowner's assoc. Once all that's out of the way, you need:

• budget and overall layout
• have licensed electrician do all the electrical work

Once that's done, use insulation boards on the walls and free standing cooling and heating modules. That way you don't have to tap into your existing and perhaps have to beef it up to accommodate another sizeable space. Happy DIY'ing!

Is the garage unfinished, meaning exposed studs and rafters? Or finished with sheetrock? Here are some ideas on how to insulate!

https://www.familyhandyman.com/garage/garage-remodel-tips/view-all/

https://www.hgtv.com/remodel/interior-remodel/garage-insulation-basics

http://howtohomeinsulation.com/insulation_projects_garage_insulation.html

You may still need a portable or window ac unit and a heat source.

Perhaps a space heater in the winter & a box a/c window unit in the summer

What are the walls and ceiling in the garage covered with? Can't you have some insulation blown into the walls and ceiling areas? That's what I'd do before I started building shelves with cubbie holes to organize all my sewing machines, materials, thread, patterns, and tools.

Head to your home center and in the section with insulation, you will find materials to insulate the inside of your garage door. That will be the start of your transformation. Next, make sure you don't have drafts around the garage door seal. You can either cover the entire wall with drywall or just tape over the gaps. Since I don't know what your seasons are like, the only other advice I have is a portable A/C unit (we have a rolling one in our work shed) and a ceramic heater for the winter. It will be more efficient to use these devices because you only have to plug them in when using your sewing studio. It's great that you are planning instead of jumping in and then going overboard. Remember that the shelves you use and other materials will also be insulating!

Insulate it, my choice is 1-1 1.2" thick rigid foam insulation. Then you can get one of those interlocking foam rubber floors . Add one of those radiator style space heaters in winter to make it cozy.