Gas forges can maintain temperatures of 980-1200°C / 1800-2200°F for long periods of time.
(Although this is cooler than the 2925°C / 5300°F that oxy-MAPP torches can reach — oxy-MAPP producing the hottest temp I can achieve in my apartment — forges are better for doing real work like forge-welding. This is because forges can bring a large work-piece up to temperature and hold it there for more than an hour, which an oxy-MAPP torch simply can't do. I think the distinction here is between temperature and work?)
There are lots of pre-made forges. The ones that are designed for making knives might be large enough for me, I'm not sure.
Propane fuel tanks:
Forges are typically powered by 20 lb propane tanks. However, the safety rules with most portable tanks is clearly "Don't store propane tanks inside your home or vehicle". This basically prevents me from using 20 lb tanks. (An aside: Some sources say that storage in a well-ventilated garage or shed is definitely acceptable, while others say storing a tank in these situations is never acceptable. YMMV.)
However, 1 pound propane tanks are normally sold from inside hardware stores and camping stores. Given the strictness of insurance for retail buildings, I would think this is okay for me too.
Note that stores often have ~6-8 of these tanks on the shelf at a time, so their risk exposure is more like 6-8 pounds of propane.
On the flip side, note that big-box stores have much better ventilation than residences, and don't usually have anyone sleeping at them.
Propane forges typically consume 1 to 3 pounds an hour, making this a feasible (if annoying) way to supply the forge with fuel. I might want to dig into the details of specifically WHY indoor storage of propane is risky, and whether storing multiple 1 lb bottles, perhaps distributed in different parts of a house, might be okay.