Would you like prayer or directly atk/str/def levels? I personally would favor having more prayer so that I would go to RS gold mountain giants. Following the 40s I would say hill giants for extra prayer and flesh crawlers as previously mentioned. Things won't change until the fifties when moss giants can be an alternative to hill giants. Once you reach the sixties you can even consider stronghold of security spiders.
Alright, so I want the majority of the basics, I will post what equipment I believe and in the event that you could edit it for me it'd be good, and tell me the approach, I've a vague notion but experience would help. I've 87 Magic, 80 Defense and 83 Hitpoints, if these stats aren't enough I'd likely train them let me know. Also, I am aware soloing rex may involve killing prime and supreme, so for mention my range level is 79 (80 easily), and 82 Strike and Power. I'm mostly doing this for cash, so if rex really isn't decent cash anymore/ever that would be nice to understand as well. Thanks.
If you apply the Burstinglobs buddies chat, there's always somebody who is hybridding and needs a solo mage partner to kill Rex for them whilst they kill Supreme and Prime. This usually means that you do not have to fret about Supreme or Prime whilst you are down there, unless either of you're bad at what you're doing. I'd take Tubby's set up with mysterious boots along with a Ring of Life until you're confident, then you can begin risking a bit more expensive equipment.
If there's no one in Burstinglobs looking for a solo mage, simply ask if anyone is hybridding/tribridding and can let you hop worlds out of theirs, simpler than having to kill Supreme/Prime to start your trip. Bring a tortoise and be sure you have a brew:restore ratio of 3:1. If you are able to bring 2 fruit bat pouches and scrolls for when your tortoise dies, fruit autumn is simply good for soloing Rex, then it's not really efficient in case you are hybridding/tribridding.
If you cannot get a fruit bat, then bunyip will need to do although that can restrict your excursion as it can only heal 80LP/minute. If you locate your excursions are too short using a tortoise/bunyip, then you may have to buy osrs gold paypal bring Guthans in lieu of Veracs and supplement your Bunyip's healing by attacking Spinolyps.