Heidi’s right. More of the same thread is the way to go. She put me onto the idea of two lots of regular thread and then I recently tried three and that worked well.
I bought some “embroidery” machine needles but I can’t see nay discernible difference in the eye size and so I’ve just used whatever was left in the machine. It’s not that hard to thread the needle with two, or even three threads of regular thread. trim them to the same length and lick them well! If you have an old fashioned wire loop needle threader it would be even easier
I find topstitching thread MUCH harder to get through the needles. And you buy lots of different colours of topstitching thread that you don’t use again…..
The other thing I recently found was some high sheen thread and a few strands of that will give even more oomph as it shines nicely.
Your dress is gorgeous