The least abravise choice is...none. 

I suggest brushing withOUT using any toothpaste, first.
You can tell if you missed any areas with your tongue that way.
Then brush again, this time with toothpaste, either starting on the areas of your teeth which get the most tartar buildup, or on your tongue.

Choose one with low abrasiveness.  You can find an abrasiveness chart below.

Stay away from "stain removing" toothpastes. They are usually very abrasive.

Do NOT brush with regular activated charcoal powder. #1. It's very abrasive!! #2. It's going to get packed up under the gums, which is irritating to the tissue. Several hygienists in various dental hygiene Facebook groups tell about charcoal-using patients who have they have cleaned, and the charcoal comes out from under the gums in little black clouds. 
 

Be my guest, if you can stomach it. I lost my cookies when I tried it. There are other options which are almost as low for abrasiveness--and taste a whole lot better.

Personally, I prefer toothpaste without fluoride and low abrasiveness. The fluoride makes me sick to my stomach every time. I use Dental Herb, CloSys, Tom's of Maine w/o Fluoride, and Rapid Relief by Sensodyne when my teeth become very sensitive. 

More info on Dental Herb Co. below--

Tooth & Gums Essentials™ is a complete all-natural SLS-free toothpaste with essential oils and xylitol. Formulated for daily brushing to achieve and maintain healthy gums and teeth.

• Reduces harmful bacteria and inflammation
• Controls bleeding gums
• All the benefits of xylitol for healthy teeth
• No artificial ingredients or harmful foaming agents
• Professional strength formula
• Available for office distribution. Not in retail stores

Many are very abrasive because the particle size is too large for the enamel. 

I recommend Curaprox "Black Is White".  Non-abrasive. Nano particles of charcoal rated 76 on the abrasiveness scale (see button below). This falls exactly between "low abrasiveness" and "medium abrasiveness." Does contain fluoride.
Product description:
Refreshingly lemony! “Black Is White” whitening toothpaste removes discolouration using activated carbon without abrading or bleaching. Contain fluoride. Enzymatic system. 15’000 ppm hydroxylapatite. Physical blue filter; cooling sensation while brushing. No SLS. No triclosan. No bleaching agents. Made in Switzerland.