Some conversion companies have gone out of business and you don't want those. Lehman is gone and Champion trikes closed their doors but has been purchased by another individual and hopefully they can provide parts to the originals.
CHAMPION TRIKES OF ARIZONA | MOTORCYCLE TRIKES | TRIKE PARTS | TRIKE KITS
Companies in business: Motortrike, CSC, Hannigan, & Roadsmith.
Do you want long wheelbase or standard?
If you plan to travel, you'd want an auxiliary fuel cell.
Raked triple trees for steering are a must.
Do you want a GL1500 or a GL1800 trike?
Solid axle or independent suspension?
Independent suspension gives a smoother ride, as does the long wheelbase conversions.
Take a test ride on a few trikes at a trike shop and see what you feel comfortable with.
Take your time and you'll find the one you want.