I went for the OEM Surface Pro Loop as sold on the link provided by
@Confuse123 here:
https://www.ebay.com/itm/302305159875
BUT, I didn't like the slightly crooked way the pencil seemed to sit in the photos, so I went for 2 loops (they were expensive, $15 each with shipping to the UK! (But still cheaper than losing the pencil) - works well, the pencil sits straight, still charges, in spite of the small gap that there now is there between pencil and ipad - I've tried to show this in one of the photos here.
There is still good feedback as I slide the pencil in the loops to indicate it is centred properly and charging on the magnet, that's useful. And I can still put the pencil on to the charging point without putting it in the loops, so good for when I am working at my desk all day, and using the pencil a lot, on and off (and there's really no risk of losing it). Having to put the pencil back in the loops a hundred times a day would be a pain.
The loops are stuck nicely to the ipad, not the magic keyboard, and the iPad can still attach magnetically to the keyboard - charging the ipad and keyboard working well. There are slight indents in the case (see photo) but they don't seem too bad, and I don't think they will cause permanent damage.
Sticking them to the iPad, not the magic keyboard allows me to leave the keyboard behind and still not risk losing the pencil when I am out and about. I also worried I would permanently damage the soft felt magic of the keyboard if I stuck the loops to it - I also don't think they would stay stuck for long to that fluffy surface.
Was very easy to install - I put the pencil in the 2 loops, got the spacing right, stuck it to the charge point as usual, then stuck them down - much easier than installing a screen protector!
So, thank you very much for the suggestion! Very good idea! Cheers, Nav