There are a few “ retail “ bagged medium choices for autoflowers .
I ran a thread on this ( fox farms ocean forest ) below in signature. However , there are other good options.
Fox farm Ocean forest is a very nute dense bagged soil. It
alone can carry feeding / growth of an autoflower upfront for 4-6 weeks , on water alone.
Most autoflowers need under a 100 days - so this soil will ride it out with minimal effort. As the autoflower consumes and exhausts this medium all you would have to do is either TOPDRESS with more Fox Farm or a good dry fertilizer ( scratched into the top soil then watered in ).
It can be a little “ hot “ upfront on some young seedlings but if you just let the plant acclimate / control your watering ( not overwater ) it will be fine.
‘This is where most growers screw up with FFOF soil , they see a little burn or some stupid blemish and they throw more crap in to it , or overthink what’s happening. I have played around with tweaks to soil ( in thread ) but if you want to just run it basic then this would be fine.
No RO / Distilled or other BROSCIENCE water - Use TAP Water. No gas off ( 24 hours ) is necessary either as plants do use some chlorine in their growth. FFOF has ph buffers in it to make watering pretty easy - no ph measuring or whatever. I live in the West Coast and my water is hard as fuck - 7.8 ph and 350 ppm and it works right from the tap.
Dr. Earth soils are also another fine soil line to use. So is their Dry Fertilizer- Home Grown or Premium Gold / Flower girl for bloom.
Promix / Sunshine #4 are good peat bases to use but will need some feeding.
Recipe 420 is probably my current favorite to run ( good amount of nutes - not too
hot 
)
This is also a good “ water only “ mix just milder. So some amending will be needed as plant grows.
You can also put FFOF in bottom 1/3 of your plant container ( kind of like a Super Soil in use ) and Top Fill with the Recipe 420.
Easy Peasy
Autos are pretty basic - plant and play. Give it 20/4 ( 24/0 or 18/6 option ) light cycle. Grow it in either 3 or 5 gallon size to give it plenty of growth potential. It will grow into a Xmas tree shape but you can do some LST training to open it up and let more light in.
There is more to talk about but reach out if you like.
Many other growers here will help you too.
