wearwell wrote:Just been told there is a pneumatic button operated system used by mountain bikers.
Anybody know anything about this, or other suggestions?
The thing you've been told about is a 'dropper post.' They are usually cable-operated, and most have a gas strut inside - similar to what lifts cars' tailgates up - which is locked when the handlebar lever isn't being pressed. Once you've pressed the lever, you can press the seat down as required with your backside, or if you take your weight off it, it will rise back up.
They're hugely important for technical mountain biking, but I don't know whether it's the best solution for what you want. You can get the things for around £100 off eBay etc., but presumably your frame doesn't have through-the-frame cabling, so you'll need to buy one which has an externally routed cable. You'll also need to find one that fits the diameter of your frame's seat tube. You'll also need to check that the post can drop down far enough inside your seat tube so that, at it's full extension, your seat is where you want it. You'll also want to make sure the operating lever isn't going to clash with your gear levers - there are two different types, and you have to select the one that's right for your gear levers. However, as you won't be using it for its intended mountain bike use (where it's important to have it situated close by your thumb) you could actually site the lever on any available bit of handlebar or frame.
A good starting point would be an 'Ascend 2.' These are made in China and badged up by various different manufacturers, e.g. Brand X and Tranz X:
https://www.chainreactioncycles.com/brand-x-ascend-ii-dropper-seatpost/rp-prod159176