Like others have said
"mids" isn't a type or strain of marijuana, it's a street term used to describe weed that's mid-grade or middle of the road; meaning it's not schwag but not killer sinsemilla either.
As for the height of your plant? A plant's height depends mostly on the strain of the plant you choose; although if you are growing indoors you have alot of control over that variable. For instance if you are growing a strain that is known to get tall, you can induce it into flowering earlier while it's still rather short to control height. Doing this though will effect your yields(the amount of bud you harvest), this is especially true for buds known to be less dense like certain Sativa strains.
If you want to grow something that isn't highly potent you could just plant some seeds from a bag of some half way decent weed that you purchased. You could also purchase beans for a strain that has a lower THC content.
Another variable to consider, other than the strain, is how the plants are grown (type and strength of lightning, growing medium, nutrients, etc), the skill of the gardener (not all gardeners are created equal), and how the final product is dried and cured. Prper drying and curing has a major effect on the potency of the final product. For example both of us could grown the same strain from clones and if you throw all your harvested bud into a pile to dry and I dry mine and cure it properly, mine is going to be better. This is because some of the THC on fresh marijuana is in it's non-psychoactive acidic form, proper drying and curing converts the non-psychoactive acidic compounds into psychoactive THC.
Here are some strains with lower THC content that I found:
Barney's Farm Seeds: Phat Fruity 12%, Red Cherry Berry 14%
Dutch Passion Seed Co: Trance 11%, Voodoo 8%, Khola 7.6%, Skunk # 11 8%, Ultra Skunk 11%, Green Spirit 6%, Purple Star 6%, Californian Orange 8%
I'm sure there are more, in fact I know there are more with lower concentrations like the ones listed above but I'm not patient enough to look any longer!
EDIT: I forgot to add that if I were taking the risk to grow plants, it would not be for mid grade marijuana. The reward must be greater than the risk. Just my honest opinion.
