Hi there, any triangle will help get your verticals perfect. This is the one we use for lettering/drafting in class. We use it with a parallel bar on the drafting table itself. The idea is to move the triangle along the writing surface, using its straight edge to write the vertical parts of letters.

Alvin 14" Smoke-Tint Triangle 30°/60° https://www.amazon.com/dp/B000HEQN8M/ref=cm_sw_r_other_apa_ahfcyb4XRYYP5

Here's a YouTube link to get you started :) https://www.youtube.com/shared?ci=ASwDZ4uleTg