Replace Tabula Rasa with a 5-link you can afford. Look for resistances, +health or +%energy shield and a % increase to your secondary defenses depending on your build and check which support gem hurts the least to lose in terms of dps or survivability.
Try stuff. If you don't like the armor just sell it again.
I know that it feels weird to lose a gem in a setup if one is used to level with a Tabula Rasa but at a certain point in the game dropping a gem slot for additional defense is definitely worth it (you won't deal damage if you're dead).
So depending on how tight your budget is, I'd suggest looking for a decent body armor with 5 links. The body armor is usually your most defensive item in a build so while having a TR is good offensively and for quality of life, your survivability suffers from it which is noticeable in later stages of the game.
Now for stats you should look for: It usually depends on your build. Are you life based with evasion or armor? Both? Are you a low-life energy shield build? A CI build?
Here's the general priority for buying a chest armor:
- +% elemental resistance (if not capped)
- Main surival resource (+max life/energy shield)
- +% increase of secondary defense (armor/evasion)
Now please note that while your chest armor shouldn't be your primary source of elemental resistances, you should ALWAYS cap out on all elemental resistances (75% by default). You can also reach the cap by using potions and since you should be spamming those at that stage of the game it should have a 100% uptime.
The cool thing in PoE: There is no such thing as soulbound items. If you aren't happy with the performance or the playstyle with a newly bought item you can just put it back on the market and sell it for about the same price (usually a minor loss though). This means you can spend your "fortune" without major risks.
Keeping some of your currency is still a good idea though since it allows for flipping and buying other items you may want which brings you closer to your end-game goal (6-link Belly in your case).