I'd go with the Corsican mint......creeping thymes would really prefer to be in full sun and a northern siting with minimal winter sunlight is not going to be their cup of tea :-) Ask at your local nursery/garden center for the availability of growers flats. These are solid (no pots) flats of groundcovers that are typically used by landscapers, although helpful for homeowners with large areas to cover. They tend to be about 1/2 the cost of potted plants. With low, mat-like, root-as-they-go groundcovers, you can just separate appropriately sized plugs and plant in between the pavers. Each plug will have enough roots for the plants to 'take'. And you can space the plugs to fill in according to the spacing of the flags and your needs, not by some prescribed spacing that may not apply to your situation. Groundcover seeds are not easy to find but that would be an equally inexpensive approach although much slower.

I'd go for mint. I've never had/seen a lavender act even remotely aggressive. Other "aggressives" to consider in addition to the various mints, that should work in your situation: Oregano - I've found it MUCH more aggressive than mint. Creeping Thymes, though not too aggressive, they eventually spread pretty well and keep down weeds. Daylilies - almost as bad as oregano. Houseleeks/Hens-N-Chicks. Again, not terribly aggressive, but eventually form very tight mats that weeds cannot penatrate. And there's lots of different kinds to try. Shasta Daisy. They stink, but they look nice, and will spread very aggressively. Wormwood - some of these self-seed very aggressively and have very grey, fern-like foliage.

While I am truly loving the lavender side discussions, we have strayed a bit from the OP's issues, so hopefully we can do both. JZ--first, where are you located? It will help us a little in knowing what conditions you have. If you're going to stick with Houzz past these issues, adding it into your profile so it auto appears can be helpful. How big is the bed pictured, and what kind of sun does it receive? Second, in addition to the light issues, your little garden has some others to address, but please don't take this as discouraging. It's pretty small for the number of plants you have in it. Many think that herbs can always be grown small (and you see pics of these adorable little windowsill or mini gardens), but reality is that most can get quite large and need their space. There are also those that need lots of water, and those that NEED drainage and can be more drought tolerant when mature. You have a mix of both in your bed. Basil, lemongrass, parsley, cilantro, and mint like water and more moist conditions (though still need drainage, not bog). They also tend to be faster growers. Oregano, thyme, sage, and lavender need really good drainage, and grow slower. When mixed in a bed this close, they tend to get overwatered and subject to issues like root rot. Cilantro doesn't like heat, or transplanting. Best to grow from seed. Parsley is similar, though it tolerates heat better. Mint spreads by underground runner roots and will eventually choke out all the other plants nearby. It can be tough to contain in-ground.

hi all, i appreciate the replies! floral-uk - thanks for the info! I am learning a lot. All the plants are actually planted outside in soil. I took some cuttings hoping to propagate them so I could use them to cook so that’s why some pictures show them in containers. the basil- we ended up digging it up and throwing it out. It was covered in black stuff (likely honeydew) and ants. Plus it was straggly and riddled with holes. RIP the “mint”/“lemon balm”: when leaves are crushed, some of the plants smell like mint, others smell like a citrus/lemon so I assumed they were lemon balm and mint. They certainly look part of the mint family and smell like it. the “thyme”: I think you’re right and it’s simply some weed lol my mom was convinced it was thyme but after visiting my local nursery, I’m beginning to think otherwise the “oregano”: has a VERY strong oregano scent when crushed. It also flowers like oregano (saw some in the local garden center). But oddly, my “oregano” has reddish stems and is more hairy. Doesn’t look like wooly thyme. It doesn’t look like any variety I’ve seen. The ones in my photo are actually quite fuzzy/hairy. Do you think it’s marjoram? Marjoram is supposed to taste like a milder version of oregano since these are outside in my mom’s garden, I still think they are worth salvaging (with the exception of the faux “thyme”) since I have to determine the appropriate next steps. She has a ton of other plants in close proximity and I would like to help revitalize them, if possible. As a preventative measure, I sprayed some of them down with a mix of neem oil, Castile soap, and water. They haven’t died yet! please let me know if you have any guidance! Thank you