Improving my Razer Blade 15

You can upgrade the storage with any m2 nvme or ssd like on this list, only one with cooling house like adata might not fit well due bottom lid that doesn’t have much room for the thickness. I personally use Samsung evo970 1tb since it’s nvme that a bit faster than default 981pm I had on Blade, however on boot time or gaming loads you won’t notice the difference even using non nvme, Intel 600p or Samsung evo860, you’ll notice only on benchmarks scores (or maybe gb copying tasks), if you want go better price for storage capacity those cheaper options are worth to consider.

On advanced model it’s only one m2 slot because there’s no room for that due advanced vapor chamber and bigger battery capacity, base model that doesn’t have vapor chamber and same battery size instead has dual storage m2 (default nvme) and (empty) sata/hdd bay. But there’s external hdd solution, I mostly store steam games on 2,5 external 5TB portable seagate on Blade 15 and 1tb SanDisk Extreme Portable ssd for Blade stealth storage expansion.
Hope it helps your decision.