Typically you should buy the larger size that accommodates the widest part of your body. It's far easier to cut clothes down than to let them out. Pear-shaped women are well aware of this. But your "apple" shape presents other challenges. The torso area could be complicated to fix without ruining the design.
Ideally you should buy two sizes and before you pull off the tags, let a tailor determine which garment is easier to adjust. The tailor will factor in how stretchy the fabric is as well as the seam allowances.
There will be certain garments that can't be recut and maintain the integrity of the style. A good tailor also will tell you that. Return the garments you don't want immediately and take advantage of free round-trip shipping that most retailers now offer.
One dress silhouette that might serve your figure better is a variation of an A-line dress: a drop-waist style, a flattering cut that avoids the waist-cinching seams that can be harder to alter.
When shopping online, keep a tape measure handy and watch out for clothes labeled "modern" or "contemporary" fit, which suggests a narrower cut through the torso and the high hip. Read the customer reviews on these items as other shoppers may warn you to size up or down in certain styles.
Surely there are certain labels that fit you better so try to stick with them. This will minimize the hassle and expense of extensive alterations. Yet our bodies are uneven and sizes are all over the map, so most garments still need tweaking.
A modest wardrobe of a few perfectly fitted garments is best. Budget for alterations whenever you go shopping. I plan on at least $50 of alterations on most dresses, maybe half that on skirts. A difficult jacket that needs lots of work could be $100. I never get a good fit in pants so I tend to avoid them, unless they are leggings. Even cheap knit tops look better when you crop them at the waist—neat without having to be tucked in.