Welcome to Goy. Corms do need to belifted and kept indoors over the winter.You canalso get begonia sempervirens from mostgarden centres or mail ordernurseries which can grow as tall as 12" If you want corms which will give you big flowers on big plants the link will let you see a variety of top quality bedding and show begonias. You may have seen them at Chelsea. http://blackmore-langdon.com/

You can get "Bedding" also known as "fibrous rooted" begonias (Begonia semperflorens) which are annuals - just for one season only. I've tried overwintering these and failed. They're not all that expensive.

I find the larger begonias that come from corms are better for planters and baskets - they're a bit floppy for bedding out.