As mentioned above, try and sit on one before you buy.
When going down the replacement seat route I tried the following on a GSA.
Airhawk - OK but a bit of a faff and not really secure to leave on the bike.
Touratech GSA single seat. - Not great for me.
coversion to standard twin seat set-up - much better than the GSA plank and TT jobby. Seemed better than the airhawk on the above for me too.
Second hand corbin front- Much better than the above but unfortunately not quite the right shape for me. It seemed more suited the fuller derrier

Sold for waht it cost me.
Yes they are very heavy and yes they are expensive but what price comfort???
Sargent front -Ahhh, true comfort at last. Fits me better than the corbin and is lighter and better made.
I had the corbin and the sargent at the same time to allow back to back comparisons. The twin seat conversion is a good place to start and is very easy to do. It can be done in an hour no problem, 30 mins when you know what you're doing.
It's one of those subjective topics, whats right for one person may not be right for another. When you find the right one though it transforms long distance riding
