Different people have different allergies to different things. The significant majority would not be allergic to the sleeping suit. I don't think you can blame SQ here, unless you can prove that many other individuals were allergic to the same suit, and SQ did nothing about it. At best, SQ might give you something as a token of goodwill but if I were them, I would just send a letter of apology without admitting any responsibility.
If you went to a restaurant, and developed an allergy to something you ate there, would the restaurant be responsible? No...just your bad luck and you have to avoid whatever you ate if it can be identified.
I have worn sleeper suits before with no adverse effects. The doctor said there was probably cleaning fluid either left as a residue on the sleeper suit or the chair. I don't think that is acceptable for a first class ticket.