There are several challenges here:

1. Driving on the left side of the road when you are used to the right.
2. Driving a RHD car when you are used to LHD.
3. Driving a manual car (with the shifter on the 'wrong' side) when you are used to automatics.

Of this, only 1 is unavoidable. From personal experience (four years in the UK with a continental car), sitting on the outside of the road is only a marginal problem; you can see ahead well enough from where you are and only occasionally it is an inconvenience when you need to pass a stopped van or at certain junctions.

Driving a car with the wheel on the other side presents several challenges:

1. The rear view mirrors are all in the wrong positions. You get used quickly enough but in an emergency your instinct is to look to where you are used to finding them.
2. The distances are all off. It is extremely difficult at first to evaluate the distance to the far corner of the car.
3. Your brain is used to seeing your lane from the left side of it. When you drive a RHD car your head is situated to the right of the centerline, and your brain notices that something is wrong. You will constantly drift to the left side as you try to compensate for that without even noticing.
4. (Manual only) There is a (hard) door where you are used to finding the shifter. You will constantly hit your door with the right hand when instinctively reaching for the shifter. It goes from annoying to painful real quick.

From what you say, I'm assuming you lived for ~50 years in the UK before moving to the continent, so it will probably be much easier for you to reacquire all those skills than it would be for others.

Going back from automatic to manual may or may not be difficult, it depends on the person and how long you drove one type of cars or the other.

Personally, I would bring my own car for peace of mind. Just remember that if you are considered a resident (more than 180 days), you are not allowed to drive a foreign registered car and it may be seized and destroyed.

There are several challenges here:

1. Driving on the left side of the road when you are used to the right.
2. Driving a RHD car when you are used to LHD.
3. Driving a manual car (with the shifter on the 'wrong' side) when you are used to automatics.

Of this, only 1 is unavoidable. From personal experience (four years in the UK with a continental car), sitting on the outside of the road is only a marginal problem; you can see ahead well enough from where you are and only occasionally it is an inconvenience when you need to pass a stopped van or at certain junctions. As per Dennis' comments, some people find it easier to remember what side of the road to drive in if the steering wheel is located at the "proper" side of the car (i.e.: RHD for UK, LHD for France).

Driving a car with the wheel on the other side presents several challenges:

1. The rear view mirrors are all in the wrong positions. You get used quickly enough but in an emergency your instinct is to look to where you are used to finding them.
2. The distances are all off. It is extremely difficult at first to evaluate the distance to the far corner of the car.
3. Your brain is used to seeing your lane from the left side of it. When you drive a RHD car your head is situated to the right of the centerline, and your brain notices that something is wrong. You will constantly drift to the left side as you try to compensate for that without even noticing.
4. (Manual only) There is a (hard) door where you are used to finding the shifter. You will constantly hit your door with the right hand when instinctively reaching for the shifter. It goes from annoying to painful real quick.

From what you say, I'm assuming you lived for ~50 years in the UK before moving to the continent, so it will probably be much easier for you to reacquire all those skills than it would be for others.

Going back from automatic to manual may or may not be difficult, it depends on the person and how long you drove one type of cars or the other.

Personally, I would bring my own car for peace of mind. Just remember that if you are considered a resident (more than 180 days), you are not allowed to drive a foreign registered car and it may be seized and destroyed.