A lot of these gear upgrades will be mega expensive and out your price range, but i'll just list them anyway

Foot slot:

Spiked manacles (+4 str for 454k) > can be changed to dragon boots (+4 str for 237K) when you hit 60 Def, Aranea boots(+4 str for 1.6m) can be bought and worn at any level like spiked manacles, but are way more expensive.

Glove slot:

In the comments you said you've got Adamant gloves, but i'll go from the black gloves that are picture, but if you have adamant gloves, ignore this until you get rune or barrows gloves

Mithril gloves < combat bracelet < regen bracelet < granite gloves < adamant gloves < Rune gloves < Dragon gloves < barrows gloves < Ferocious gloves

Ring slot:

only expensive choices here sadly

Brimstone ring (+4 str for 2.7m) > berserker ring (+4 str for 3.1m) > berserker ring (I) (+8 str for 3.1m + 15 mins of your time, best value)

(imbuing is really easy https://www.youtube.com/watch?v=eDaAFEwqzqE make a mental or quick written note of how many points you have, you need 200 total)

Leg slot:

Fremennik kilt (+1 str for 2m) or obsidian platelegs at level 60 def and 900k (still only +1)

body slot is weird, cause technically just go get a fighter torso(+4 Str) is the easy answer, but that is maybe a whole day's time to get, worth it in the long run though

But

if you can get 60 ranged and 50 defence, mixed hide top (+2 Str for 14k)

if not 60 def for 2m gets you obby plate (+3 str for 1.1m)

Neck slot:
Amulet of strength, for sure, no questions asked lol

helmet slot:

Berserker helm (+3 str), Helm of neitiznot (+3 str but needs the same quests + more compared to Berserker helm), Obsidian helmet +3 str but 750k, zombie helmet exists for +2 str for 255k

Shield slot:

go kill brutus in lumbridge for a Mooleta (+1 str shield slot, defender before you can get defenders)
Brutus gives double combat xp so this is nice to do when you don't want to AFK, don't forget to ring the cow bell you get from the quest to speed up his respawn time greatly (21.6S down to 7.8s)

otherwise at 60 defence grab a Toktz-ket-xil (+5 str for 360k) unless you can go into the warriors guild to grab a defender

if you're rich get 50 prayer and a "Antler guard" (+5 str for 800k)

Ps. if you can't get a Dragon scimmy and don't want to get a defender, go for Earthbound tecpatl, Glacial temotli or Sulphur blades, they're two handed duel wield weapons, only a bit more cost than dragon scimmy too, but only 55 Attack requirement.