The major differences will be in two things: fabric and variety.

As a member of the lower middle class (not a peasant - that term implies agricultural labor), you would generally have been wearing linen/hemp, cotton, and wool. Linen or hemp in a medium weight would have been used for your underlayer, whether a woman's shift or a man's shirt; typically people just say "linen" here, but hemp is indistinguishable from linen and it's likely that many items considered linen in museum collections are actually hemp. Cotton was coming into use for this purpose in the Americas, but my understanding is that Europe's linen industry was very entrenched and of course local, so it still had the upper hand on the continent and in Britain. For both genders again, you would be wearing knitted stockings of linen or wool, depending on the season.

If you're a woman, you would wear a corset, petticoat(s), and a gown. It's debatable around this time whether women of the European peasantry would be wearing corsets rather than more traditional clothing or simply no supportive garments, but as someone living in some sort of town, you would most likely be wearing one, although it might be something more homemade and experimental. Your gown would be a printed linen or cotton, or wool. If you're a man, breeches, waistcoat, and coat of linen or wool. These materials would generally be chosen based on the season, unless you were too poor and had to wear cotton/linen in the winter as well. You might have a "best gown/suit" for special occasions and mass on Sundays, and then an ordinary gown/suit that you wore on all other days until it wore out. You would probably have a single hat or bonnet, and a single cold-weather outer layer - a cloak if a woman and a greatcoat if a man.

On the other hand, once you've been elevated (though I would note that a) "nobility" has a specific meaning, and marrying into a rich but untitled family would not mean rising into the nobility, and b) poor men did not have the same opportunities for marrying up as poor but pretty women, as wives typically took their husband's social status), you could expect some changes.

Your linen would get finer, for one thing. Very lightweight linen underclothing was a status symbol, with especially sheer varieties used for the ruffles on men's shirts. Your corset, if a woman, would be made in the newest style - a column given shape with triangular panels at the bust and hips, and a row of bone eyelets down the back.

All of the fabrics used in your clothing would become more expensive and finer as well, but more strikingly, you would change clothing multiple times a day and have access to all sorts of specialized outfits for particular occasions. At a minimum, you would wear one outfit for the morning - something not too unlike what you wore as the child of a baker, but in better repair and finer versions of printed cotton or wool; if a man, you might try out the longer and tighter breeches coming into fashion, or even some tight buff pantaloons - and then change into full or half dress for dinner in the early afternoon. If you were a woman, your evening dress would consist of a silk gown with short sleeves, possibly with a sheer overlayer to it, although it would likely not be heavily embellished. If you were a man, your evening dress might be silk or very fine wool, and your suit would have breeches and white silk stockings, which you would wear with black evening slippers.

In addition to this, you would have a selection of day and evening clothes to choose from every day, of varying levels of formality and opulence depending on what you were doing and who you were doing it with. You would also have clothes specifically for riding and going on walks, and your choice of outerwear and headgear to match what you were wearing. If a woman, you would have lightweight muslin canezoux for the summer, heavier spencers for when you wanted more warmth, and pelisses, douillettes, and witzchouras for when you really needed to keep warm.