What is the best Shower Gel for sensitive skin?

[Biglips]

as my skin had seems to be dried out and ive got a bit of exzema on my back. ive been using Imperial leather blue shower gel but possibly its too strong for me

Try water only. Unless you get really mucky.... I use coconut oil under my arms and around my groin and just wash with water. My skin is so much better, and I promise I don't smell!! People find their skin clears up when they stop using shampoo, too.

It may not be as straight forward as suggested?
There are two issues, not entirely unrelated.
First, perfumes are, by their nature, often ketones, aldehydes or related products. These are the substances especially capable of activating [it's the old lock-and-key explanation in chem/bio/med books] the odour sensors in the nose/sinuses.
The other culprits are the commonly used preservatives based on methyl- and chloromethyl-thiazolinone {oh yes, look at the label!}
All these substance can (eventually) trigger allergic reactions.
Notwithstanding, allergies are a moving target. Some folks can go through life without falling prey. For some unforunates, they may experience instant adverse reactions.
For many, however, allergy may be delayed for years, even decades before it strikes.
All this information became apparent to Jo Public around 20-30yrs ago in the USA. The joke amongst the cognoscenti was that manufacturers leaving OUT such constituents charge more for the privilege. In truth, not quite so simple, but one get's the point...