You probably don't need a base, but spending money on a good mattress is definitely worth it.

I would recommend getting it locally though, if this is possible for you right now.

We ended up buying an organic mattress online (e.g., Avocado, My Green Mattress). It’s made a huge difference.

After doing about a month of research (The Mattress Underground is a good forum) I bought a latex mattress from SleepEZ. Had it for a couple of years and been very happy with it.

One consideration to keep in mind is that if you sleep in the middle of your bed you won't want to get the split layers. They make assembly easier and allow for more granular customization, but a friend of mine who got the same mattress feels the crack between them where the layers separate slightly.

After the birth of our daughter my wife and I got the Beautyrest Black. The improvements to our sleep and general well-being have been amazing! https://www.beautyrest.com/black/k-class-ultra-plush-pillow-...

A latex mattress topper works great, in my (& a relative's) experience, upon a good old mattress. 3", medium-firm, pretty reasonable cost, just lay it on top. I like using enough layers of sheets so as not to feel the dimples/holes. Natural latex foam, it's surprisingly cool and solid to the touch, like a chilled custard.