I've been using cases on my macbooks for the last 6-8 years, and have owned airs, pros and 12" macbooks (which I currently use). I've tried the cheap unbranded ones from ebay, speck, incase, tech21, and more recently Jetech from amazon.
Speck have always been prone to cracking- their newer models for the 13" and 15" touch bar models feel a bit better quality material (not as flimsy plastic) but they also feel a bit thicker.
The unbranded ones from ebay are ok- not the best looking but you get what you pay for. I could buy about 6-8 from ebay for the cost of a speck or incase at RRP so if you're happy to replace them when they crack or the foam feet fall off etc, then they're not bad.
Tech21 is nice and well made, and also adds an extra layer of impact protection so this may be the one to go for in your situation.
I've been using an Incase dots shell on my macbook 12" for the last 2 years and for me it's easily the best quality. Not overly thick, feels solid and well made, and the frosted finish has a nice texture.
I did try a JETech one from amazon on a 13" macbook pro touch bar for a week or so before I sold the machine on- the best quality case I've tried from a 'non-branded' (i.e speck/incase) manufacturer. Unfortunately it seems they dont make them for the 12" which is a shame as I'd probably take it over a new Incase one due to the cost.
Hope that helps.