If you are planning to tow a trailer, you are going to need blind spot mirrors for your car.
Even without towing anything, your car will suffer from blind spots. The side mirrors will only show so much of the area to the rear quarter and in the blind spots could lurk other road users.
With a trailer in the equation, the situation is worse. You may have no vision to the rear, with your rear view mirror blocked. Your side mirrors will probably give you a good view of part of the trailer, but nothing more.
Blind spot mirrors are needed to help with this problem. They come in various sorts and you will need to consider what is best for what you are going to be driving and towing.
You can get additional small mirrors that stick on your existing side mirrors. These are a strange oval type shape and have convex lenses. They are called frog-eye mirrors and although they may show the same areas, they will give a wider perspective.
There are others which may attach to the existing mirrors but are on brackets which position them further from the side of the car. They give a better view of further back and you may get some rear view capability with them. They will also help cut out some of the side blind spots.
Some blind spot mirrors will completely replace the existing with new larger mirrors on extendable arms.
You need to angle the blind spot mirrors so that their overall fields of view interlock as far as possible. Make sure they are fitted properly and will not move about in the wind caused by the movement of the vehicle. Check and note where the blind spots remain and keep them in mind when driving.