I'm also a potato, now a size 20-22 but I spent years wobbling on the cusp of the 16-18 boundary.
I found full length dresses were good, as they extend your height. Empire line is good if you have bigger boobs than stomach. I not empire then a waist tie loosely tied to pull in at the upper waist can work well.
My suggestion would be don't try too hard to look slimmer, instead enjoy your clothes. I've found lots of inspiration online on Instagram, of women who are larger sizes and can still wear bold looks.
For example , contrary to old advice, I find bigger patterns work better than smaller.
A cleavage can work well to make you feel less frumpy, and so either a wrap style or deep v neckline can be flattering.
Alternatively you can also really dress up a plain dark coloured dress with interesting accessories and shoes - so tempting to use your budget to do that.
Most brands now do a size 16, so you've got great choice. I'd go somewhere like a big shopping centre and do the personal shopper.
Another couple of tips although these are online:
Scarlett and Jo do the most incredible range of occasion wear for larger sizes - and they have countless photos of real women looking and feeling fabulous to inspire.
There are other online ones I looked at for my brother's wedding, I'll try to dig them out....