Getting back to Taipei from Taichung tomorrow night

I'm trying to figure out how to get back to Taipei from Taichung tomorrow, after 5 PM. Seems like not an ideal time with lunar new year travel. Both HSR and regular trains seem fully booked, but I'm not confident I'm using the websites properly. I'm also unclear, are there any non-reserved seats or standing room available? Wondering if anyone here might have any advice/ideas for me. Appreciate the help.