Any good brand digital blood pressure apparatus from a good seller.
Only point to be noted is buy the arm cuff BP apparatus, not the ones which are worn on the wrist. That is the BP apparatus is to be tied on the arm.
Next Steps
The first time you measure BP if possible counter check it with a doctors/health woker/paramedics record on a Mercury or aneroid BP apparatus if possible. Just to make sure it is well calibrated.