if possible I would always go for the slightly bigger or smaller needles to make the pattern fit. That way you follow the instructions for a different size than you want and get the measurements you need.
Just be careful: patterns don’t always give all instructions in stitches and rows but sometimes in inches, too. Then you need to follow the inches of the size you want to have (for example the middle of the road between your two almost fitting sizes).
22 sts and 28 rows =4" in Stockinette sts … 5 1/2 sts to the inch.
I guess this is not your own sample piece but the pattern advice? have you made a sample? what did you come out with? and with bigger / smaller needles (bigger in your case, I guess)? what will it be?
your math, anyways, is correct. 234 stitches devided by 5.5 to the inch is 42.5 inches around.
The only problem you throw yourself into is the pattern repeat:
18 stitches per repeat. Now you add in 7 extra. That is not even a half repeat but too much to smuggle into the sides. you can’t just do an almost half repeat on one side. But you can not do two not even quater repeats on each side… all will look funky.
the 18 stitch repeat is probably the reason for the big spaces between the sizes. they just add a repeat between all versions - and leave you hanging in mid air.
so the change of needle size is your best bet. Really.
I have problems with garments, too. I try to make them fit (in sewing as knitting) and I find that the wait measures that fit me lead to chest measures that are a good bit too small. And the chest measures that fit will hang loosely around the waist.
that means: I have a pretty big bust but thankfully have not put up so much weight that my waist catches up
therefore I am likely to smuggle two stitches in on each side for the bust measure. usually by just increasing under the arm hole (an inch or two deeper where you don’t see an extra stitch on the side even with patterns (your arm will be over it mostly anyways) and try to hide it whereever that is needed. then I continue that and may or my not get rid of that stitch (or two) within the armhole.
2 stitches on each side on each piece will make 8 all together and that usually makes a good difference with the pieces I made by now. with finer wool I would need more adjustment, though.
when I sew dresses both my bust and my hip size fall into the same pattern, just my waist doesn’t. I either tuck things in a little by curving the seam line or I make a belt.
So: you are not alone! truely not.