There are lot of options on the market for pure CBD, some better then others.
I'd look for one from a good company as some of the shoty ones will not guarantee the CBD content and say its "high" with out context. and some places rate CBD of 2% high.
Look for lab test results to prove they have confirmed it is genuine.
Dinafem was a leader in CBD for a good bit. Their Dinamed line is all cbd focused, I have a few of them, dinamed quick and dinamed kuch cbd auto.
As others have said below Charlottes Angel is a good pick too, this is by dutch passion.
CBD Crew have a lot of nice mixes.
Fastbuds Green Crack was ok when I grew it. 1:1 cbd:thc I liked the smells and flavour I have yet to try their 20:1
autos in general can be more picky and not always stable in terms of genetics, I'd stick with photoperiods
Royal queen seeds has a few CBD ones as well. Have not grown them out though and can not confirm how well they are.
Look for the strains/breeders on grow diaries and see if they work for you.
growdiaries.com/seedbank/dinafem/dinamed-kush-cbd-autoflowering
This is my current fav, I did not make a diary of my earlier plants but they all did well indoors.
I only have my one grow diary now trying to make seeds out of the plant as its been discontinued.
Good Luck!