You are not really going to get a huge choice as such, sidecar makers are few and far between. You really need to tell us how you intend to use the outfit, what the use of the seat in the chair will will be, what mechanical skills you have and if you have tens, hundreds or thousands to spend. If you can weld or have £40,000 to spend the choices are greater. If you have £5000 and no skills or facilities you are probably better buying a ready set up outfit on e-bay that trying to fit a chair to the Ten. Most chairs are going to really reduce the ground clearance, so going to a road style bike won't make a great difference off road. Strength will, so full steel frames are best.
The Tenere does not look a bad prospect as it has a decent frame, but for anything except occasional road use you will need a subframe. Velorex fittings will be a PITA. You need to call UNIT and Watsonian to see if they've ever made one. If they have not they will need to see your bike. Don't get dragged into the leading links/brake on the chair/not enough power debate, a Tenere outfit would be unusal, perfectly usable and great fun if done right without.
If you want a chair to match the style of the bike you want an ETH from UNIT, but they are perpetually in the process of going bust, so don't expect fast service. WASP could build you a chair but again you'll pay and wait.
Ural chairs are relatively tough, cheap and available but have ball mounts meant for Urals. These will need cutting off and replacing with something that'll fasten to your subframe. Talk to David Angel at F2, he does Ural to bolt fittings.
What you don't really want unless you can get a lot of strengthening added is something like a Velorex. A chair designed for a 20 HP JAWA will not like 48HP and off road use, it may take one or the other.
The platform chairs like the ETH, WASP and similar are meant for adults who'll help out on the rough stuff. Your kit still gets wet just like on a solo bike and you cannot carry your 85 year old Aunt, small children or dog. Choice is of course personal, but I always preffered some sort of box. There is little to stop you converting any chassis into a box or platform.
These might give you ideas https://sites.google.com/site/yorkshireoutbacksidecar/
I am an ex-sidecarist. After ten years on three wheels the various insurance and MOT hassles took the fun out of it and I'd rather spend my reduced spare time riding. I will be back when time allows though, it is a very different experience to riding a solo and a lot of fun.
I can save you a trip to the other forum BTW: They'll tell you to buy a Ural!