For indoors on a windowsill I would look for orchids that bloom often or stay in bloom a long time. Don't worry if they have small flowers instead of giant colorful blooms. Look for phals that have a reputation for staying in bloom a long time. Sequential blooming phals, which are usually summer bloomers, only have a couple flowers open at a time but some, like my Dtps. Purple Martin 'Champion', can stay in bloom for more than six months. Look for compact growing cattleya crosses that bloom more than once a year like Brassocattleya Hoku Gem 'Freckles' which blooms several times a year. My Blc. Hawaii Stars can bloom four times a year. Paph Pinocchio has a reputation for blooming for long periods of time, in some cases more than a year. Good luck in your quest.