Wrist BP cuffs are now inexpensive, accurate workhorses. So accurate they are being used in large hospitals.
Walgreens has a wide choice and one of the least expensive is at Amazon has the Omron 3 series, an elegant little wrist cuff and the least expensive.
Buying one that shows at least the last 5 taken, preferably with a graph, gives you fascinating proof that you are retraining your blood pressure down. (Retrained mine from 150/105, scary, to 105/60 within days and it’s stayed in that low range for 9 years, through thick and thin, without doing anything more.)
Blood pressure is a closed pressure system, a fixed amount of fluid volume running through a fixed system of pipes. If you contract all of your muscles, with great force, for example, the lumen of the pipes will compress, and the same amount of volume will be forces through a smaller space. When taking BP at home, sitting on a chair, prop your feet on a stool to remove pressure from the back of your legs (or sit on the bed, or stand up) and put your wrist at the level of your heart. This gives the least blood vessel compression to large body areas and greater accuracy.
Postings in the Blood Pressure and Stress categories on the sidebar give more information.