The single change that matters most is separating the screen from the keyboard, and it is also the cheapest.
A laptop forces one compromise: the screen is at hand height, so either you look down all day or you type with your arms up. Your neck ache and your wrists are the same problem showing up at both ends, which is why fixing one at a time never works.
So: raise the laptop until the top of the screen is roughly at eye level, and put a separate keyboard on the table. Anything that stacks works for the riser — a stand, a box, books. The keyboard is the part you have to buy and it is the cheapest useful thing in this whole discussion.
What that gets you immediately:
- Head upright rather than tilted forward, which is most of the neck ache
- Forearms roughly level, which is most of the wrist problem
- Elbows at your sides instead of out in front
Order of value for your situation, having done exactly this:
- Separate keyboard plus something to raise the laptop. Transformative.
- A cushion on the dining chair to raise you, so your elbows sit at table height instead of below it. Dining tables are too high for most people to type at.
- Something under your feet if the cushion leaves them dangling. A box works.
All of that packs away at dinner time, which is your real constraint.