The Hima is not too fussy about sizing and all the old bags I have fit OK, magnetic or strap on.
Although magnetic seem to be out of favor these days, with fixing rings talking their place.
If you can find a ring for the Hima---!
Best bag I have bought is a magnetic Ogio, a long time ago and they are NLA.
Even the cheapest bags have been acceptable quality, never found much use for fancy features apart from expandable and a map pocket, if you still use maps.
So, hard to go too wrong, any brand name you recognize will be OK quality, but better if you can get to a store and have a look and pick one that suits you'
This one looks close to my old Ogio.