do you do online stickers? online stickers are pretty good as they don't cost you money to make, and if you have constant releases you may be able to build audience, and if you're lucky your sticker may hit big (in this sense it's pretty similar to webcomics), but of course, there's always a possibility that your sticker won't sale.
for example, LINE is pretty big in my country so it makes a good market to sell LINE stickers (I think you can also sell stickers on whatsapp? not sure). I do stickers for clients from time to time, and planning to work on my own brand more recently (although it's a bit hard because it has been more competiitve these days).
as for ideas, the ones that usually sell are the simple, cute or weird animal stickers, female characters (usually anime style) with cute style, male characters with cool or weird vibes, or couple stickers with lovey-dovey vibes
these are just personal reccommendations. good luck 