Hey Zee,
I am building a Fokker D-7 from Hobby Hanger 40 size, they also have a SE5a Kit and both should be great gentle flying planes.
Look into
www.funaero.com for more great WW1 kits and also Flair products,
www.flairproducts.co.uk, There are US distributors for these kits too. All the above companies have WW1 kits under 60" WS and around $100-$200 per kit.
Balsa USA has some good kits but the WW1 biplanes may have a wingspan that is over what you want. The monoplanes fit your wants.
I'm getting into the WW1 stuff and I am really enjoying building and learning about these older planes. Have FUN!!!!
Navigator