Since you said its for older laptop, i will assume its SATA3 or SATA2 and regular 7mm (maybe 9mm?) laptop size slot.
Don't bother looking into mSata SSD (even if your laptop supports them) since they are pretty much obsolete and not really made any more going forward.
Regular laptop sized SSD are still being made, along with m.2 sata3 SSD for older style laptops.
Newer m.2 NVMe laptop SSD are much faster, BUT older laptops can't use them.
m.2 is the slot type, and can have either SATA3 connection or NVMe connection, but are NOT cross compatible with each other.
back when i was doing my research for SATA3 7mm regular laptop size SSD:
1) samsung 850 pro series 10yr warranty sata3 ssd BUT VERY expensive
2) samsung evo 850 5 yr warranty sata3 ssd BUT expensive
don't bother with samsung 750 evo series (google will tell you why)
those 2 are the top performing BUT most expensive sata3 ssd
3) Crucial mx300 series (what i bought)
(slightly slower speeds than samsung 850 pro/evo BUT in regular usage you likely wont notice much difference. Definitely will see a difference of some MB/s or IOPS if you are too much into benchmarks etc but i didn't care, price was more of a factor for me since I was also going to put it into a 2 year old laptop that i use all the time still since it still has decent specs otherwise. Am I happy with the purchase? hell yeah! maybe the samsung 850 evo would make things 1s or 2s faster BUT the difference in price was too much for me at the time of my purchase. My BIOS time according to windows 10 home task manager is like 3s i think. I noticed at the time that SSD prices had gone WAY up the past year or 2. I purchased i think march/april of this year 2017)
There was others (corsair neutron xti i think?) and some other companies that you normally wouldn't hear about unless you research computer parts like mobo/gfx/ram etc but the crucial mx300 was easier to buy for me.