You can look for design firms looking to hire mechanical engineers but then you’ll be doing the same type of work but at a design firm. You can then transition to design depending on your design skills.
Keep your job and work on your design skills in order to have a bitching design portfolio. Maybe it’ll take you a year or two but it will be better than doing a job you hate for the next 30 years…
Your mechanical engineering experience would definitely be an asset to compliment your design skills. But if your design skills are not there, you will be hired to perform mechanical engineering tasks not design.
Good luck.