I have a friend who buys outdoor fabrics and makes a profit of $400 on each set of custom boat curtains she sews. I could have her call you if you'd like to talk to her. She doesn't sell on the internet, but directly to the manufacturer of the boat. She makes 2 or 3 sets of boat curtains a month along with her regular job at Joann fabrics plus selling sewn and stuffed muslin snowmen Christmas ornaments all year at farmers markets. These little snow men are "themed" in the local school colors and have little skis and snowboards on their feet. They sell for $14.95 each. She sprays glitter on them when they're complete. They have black beads for eyes and a tiny toothpick that's been painted orange to look like a carrot nose and a tiny neck scarf made of fabric. This friend also sells aprons, but I'd stay away from those unless they are "themed" because there are already zillions of gals out there already selling them.
The big bucks are in custom curtains. Have people measure their windows (draw a diagram of "how to") and give them 8 or 10 fabric choices to pick from or they can send you their own fabric that matches their decor.
Another thing that's big right now, (but seasonal) are simple tube tops for teenagers. They are super easy, and super easy to mail. You'd only need 2 or 3 sizes because they stretch. Also think about making garden hats, or "tool belts" or tool bucket belts for gardeners. At the market I sell at every Saturday, the biggest selling things are anything for the garden!
Another way you can go is to specialize in baby stuff, like 100% cotton flannel receiving blankets. It's hard to find quality 100% cotton baby and child's clothing these days and if you really want to have something special sell "green" organic cotton (and hemp) baby things. The organic clothing thing is the new up and coming "thing"!
CAUTION: stay away from clothing because it's hard to fit everyone and you'd need to carry to many sizes. But I also know a woman who makes quite a lot of money making "themed" mens' shirts, like with Harley flames, old cars, baseballs and bat or footballs on them. She spends a fortune buying rayon/poly fabrics by the bolt and just pumps them out in S,M,L, & XL. She has quite the inventory. They sell for $49 - $59 each, but like I said, if it were me I'd stay away from clothes, especially women's clothes because they are picky about the fit and fabrics.
* If you can make something that sells for under $20 it will sell quickly. People tend to "have to go home and think about" anything over $20, but if it's under $20, especially if it's under $15, they'll buy it right on the spot! Believe me when I say this because that's all I do, deal with the public at fairs and I've been doing this over 20 years.
I have seen fabric tubes for plastic bag storage sold online for 12 dollars. I made some to give to friends out of bandanas. Bandanas ar less than 2 bucks each. Just fold the bandana in half, sew down one side, make a pocket on either end for elastic. Attach a loop on one end for hanging. You stuff the bags in at one end and pull them out at the bottom like a dispenser. The beauty is .... about 800% profit on each item. And they don't take much time to do.
With Xmas coming and as a mother of 3. I am already searching on eBay for drawstring Santa sacks large ones! The ones on eBay are about 30 x 30 inches which is no use at all as a Santa sack especially when it is stuffed with things from the dollar store. So I think extra large Santa sacks with a drawstring top in seasonal colors or fabrics would be great and sell well, or how about sports drawstrings bags for younger children with or without their names put on as an extra, to use at school when they have to hang their sports kit on their coat pegs.
What about slip covers for furniture. If you are a good sewer and can make them look nice, I'm sure people would pay.