I've experimented with topicals for my back problems. I started with a complicated recipe of emu oil, Tiger balm, and some other stuff but eventually I found that simple infused olive oil worked just as well.
That means just heat the oil and trim or bud material in a crock pot on low for 4 hours. They run around 200 degrees which will take care of decarb, no need for pre-treatment. I strain the oil and then pour through an old T-shirt to filter it.
It does take a while for the oil to absorb into your skin, and it will stain clothes or sheets during that time. I'd prefer to use something alcohol-based that doesn't leave a residue or stains.
Also I'm not sure how much relief you'll get from topical, my back's innards are all screwed up from being destroyed by surgeons with power tools. The topical gives me nice warm feeling and helps with muscle spasm a little but it doesn't reach the bones in the spine that generating the pain.