I used to work at Woodmansterne for a few years so I know this industry well.

Maybe hold an online competition on your website as a way to capture the email address details of those visiting. I always tell my clients who are in the repeat order business that they need to be staying on the 'radar' of their customers and prospects using as many different methods as possible (free ones like PR and email are best.... I like free!)

I agree also that you need a simple form on your website to capture the details of those who don't buy there and then.

You need to be doing more than just driving traffic by your website. Look at other ways of marketing. Do a prize giveaway on the local radio station and local paper. I know it sounds like a lot of giveawaying but you have to think of the publicity and long term value of a customer (and as said who they know). Networking at local events if you can.

I have just finished working with a High Street Printers and he is having his best year ever (est 1974) Facebook and Twitter (i see you have a twitter link on your website) really work in a B2C environment, I would suggest if you haven't done so already you setup asap a Facebook fanpage and send it out to all your friends and family and twitter followers then use it to run facebook only promotions and drive traffic to your website from it.

You NEED to expand the range as the others have said too, your market is too narrow unless you want this to be just a hobby. If you think about a physical store they would never survive it's just too niche.

If you don't want to stock gifts that could compliment your product range consider becoming an Amazon Affiliate (free again) and getting a commission on all products that you sell through website
A final thing its great you get letters of thanks and how pleased they are so make sure you put them on your website (with permission).

You have a goldmine with all those happy customers. Don't try and ‘sell' or push your products down their throats give them information and subtle promotional messages included in them.

I know I said final thing but you are in such a personal and emotional business so consider putting pictures of yourself online and a little biography (i saw your about us) to show how you can relate.

I hope this helps as you a lovely business and I hope it works out for you.