I've made suggestions below of two bikes of a very similar style but differing hugely in price:
Firstly, I would suggest you have a look at the Shand Tam
. It will give an upright position, especially if built up with Jones Loop bars as shown on Shand's website and you fit a relatively short stem (and request the steel steerer be left uncut to give the bar height you want). It can be built up with either derailleur gears or a Rohloff. The features that should make it suitable for the use you describe include:
- long chainstays (460mm) to give good heel clearance with rear panniers
- low stand over, something which you are likely to appreciate not just if you are not very flexible, but also in particular when you have even just a few kg in the rear panniers (the higher you have to lift your leg over the top tube to mount or dismount, the more awkward it makes controlling a loaded bike while balancing on one foot and gripping the bars)
- oversize 631 tubing to increase stiffness and resist frame flex/sway caused by loaded panniers
- tall head tube
The major downside of this type of bike is that it is not light. Because of the larger 29" wheel size and the frame being built to cope with heavy load lugging and the forces of disc brakes etc., I suspect it will be heavier than your Sherpa. It's not a bike for getting out of the saddle to accelerate or to power up a short rise - it's the sort of bike on which you tend to stay seated and just keep plugging away in a comfortable gear (a type of riding which does tend to suit a Rohloff, but which not everyone likes).
The Tam can take up to 3"/70mm tyres for off road riding, but assuming you only wanted to use it on the road and maybe on gravel tracks and bridleways, I would fit narrower tyres (on rims to suit), e.g. maybe a 50mm wide touring tyre with 60mm SKS/Bluemels mudguards.
Secondly, I would suggest you look at the Genesis Vagabond
. This is a similar style to the Shand Tam but the frame is at the opposite end of the price spectrum. It's designed just for derailleur gears, although a Rohloff could presumably be fitted if a chain tensioner were used. There are a few small geometry compromises compared with the Tam:
- chainstays 15mm shorter: not as good for loaded handling maybe as the Tam's 460mm, but as long as your heels clear the panniers it might not matter to you
- significantly shorter stack (627mm vs 669mm in the large sizes), so you would probably need plenty of spacers and maybe a steep angled stem as well (although possibly not much different from your current Sherpa)
- on the plus side given your requirement for an upright position, reach is shorter than the Tam (395mm vs 422mmin the large sizes)
- shorter front centre
You can see some photographs of a Vagabond built up by a forum member, reohn2, here
(scroll further down that thread to see the flat bars he has since fitted which have a similar sweep to Jones bars). Although it's available as a complete bike, your requirement for flat bars etc. means it would probably be best to buy it as just a frameset and build it up how you want it (or get Spa to build one up to your own spec: they are currently selling the frame for only £350
I would stress that the Tam and Vagabond are pretty niche, marmite types of bike, and I would not suggest them were it not for your requirement for what is presumably a relatively very short reach. Were it not for that and if you were largely riding on the road, I would suggest considering a conventional touring bike, e.g. a Spa Steel or Ti touring frame which they can readily build up with flat bars if required, like this
, or the 'short' top tube version of their Wayfarer
if disc brakes are required.