Hi Claire,
You've had a lot of good advice so far.
I just wanted to pop in and comment about the Wisper 705se - I really must write a review, although I have commented about my experiences and choice in various other threads. Whilst I do not suffer with chronic fatigue, my stamina is not great -partly (well probably mostly) because I'm overweight and unfit, but also because I suffer with chronic asthma which limits my lung capacity somewhat and I get out of breath easily.
When I was looking into purchasing an e-bike I test rode the Wisper Torque and the SE versions and I was, at first, quite torn about which would suit my needs better. Setting price aside I opted for the SE version mostly because I found the SE suited how I intended to ride and the type of terrain I ride on (flat as well as hilly -but not moutainous). Angelnorth has the Torque and it seems to really suit her and she's written a very informative review on her experience -but for me I found the SE gave me assistance (at whatever level I chose) when I needed it without over exerting, but when I'm feeling particularly energetic, I dial down the 'assist' and use the gears to adjust how easy (or not) the ride is. I've not had any problems moving off from a stop start because the 'assist' kicks in quickly -now it's fair to say I'm not having to deal with London traffic but I'm confident enough that it'll move off swiftly if I need it too.
Above all nothing beats a test ride and you should go try a few different brands/models out if you can