There is no way to create a full custom character without a lump editor such as SLADE. SLADE is perfectly safe and free of viruses/malware as long as you get it from the official website. I've personally used it for over a decade.
For art, you can probably use whatever art program your computer comes with, but you'll have a better time with something like Aseprite, Paint.net, or GIMP. Browser-based image editors exist but are probably not a practical solution.
Good luck making your character! (And please try to keep your thread on-topic next time -- the Report button can help with this)