In reply to Bog ninja:
The big difference on the 25 compared to 35 is no hip belt. The 35 on the other hand is huge and definitely needs one.
The two chest straps work very well, and I suspect are fine if the 25 isn't overloaded. It would probably be possible to sew a basic hip belt on, but the take off is where the chest straps arise from so tricky. I have an UD35 and it is *big* for what you want, although your sleeping bag sounds pretty huge.
Of note, the side compression straps are a bit rubbish on the 35 when it isn't so full - the steps just pull through the strap holders, kind of difficult to explain but they don't hold a half-full pack tight close to your back, all the stuff just joggles down to a bulbous bottom - perhaps reflecting their owner, who knows...
Also, the smaller model (the 15l one that Mrs B has) used to have some very poorly designed fasteners that only work one way round for the main closure. Actually, the 15 is a bit useless.
The other slightly more unusual pack out there I would like to try is the Ultraspire Epic XT, which is a solid 25l pack that is relatively "thin" so the weight is close to your back. It looks to tick a few more boxes than the UD35 (especially with a decent hip belt). A lot more 'stuff' on the front looks busy, but is good for balance. https://ultraspire.com/products/epic-xt/
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