I tried a lumbar support but found it tended to push me too far forward in the seat. I know plenty of people that swear by them though.
However, that simply reinforces the point about it being a disgrace that they are not comfortable in the first place! Would it be considered acceptable to have to buy your own GPS because the aircraft had a system that was unusable? (I'm talking about large machines here.)
The big difference we have over fixed wing pilots in this regard is that we are totally imobilised in the seat; they can walk around on a long flight. Thankfully the longest I've ever done was 8:55 in one day, but even shorter days can leave you feeling half crippled sometimes.