if you gravitate to home brew, and want a stable shelf life, I would suggest you research Patrick Gainer's discussions - mostly as old posts on this site - on a product he called PC TEA.

It used phenidone, acsorbic acid, and an organic solvent (that may be hard to find in parts of the world), Tri Ethyl Amine.
Because there is no water in the formula until it is diluted, it works quite well at staying stable on the shelf. The TEA acts as the needed alkali.

I mixed some and found it had the the same activity when it was diluted after 8 months as when working solutions were diuted when it was first fresh.

Gainer also researched using ethylene glycol as the solvent for the developing agent(s), and mixing this (a solution ) with (b solution) of sodium carbonate (and maybe some sulfite; my notes are not handy as I write this) to provide the alkali at the time that the stock solutions are mixed and diluted to the working solution. This approach allowed long term sotrage out to a couple of years for these developng solutions.

Another home brew that has a long shelf life is PMK - an a+b stock solutions Pyrogallol and Metol based developer, with sodium metaborate (Kodalk) as the accellerator. It is quite long lasting.
It takes a long time to work at 20C, and I usually work with it at 24C to keep tank times reasonable. It might work well for you. If find it makes quite nice negs when used at 1a+2b+100 water dilutions. Like all pyro formulas, it stains, so gloves are a good idea. My stock A of this went black and inactive in a half full bottle after two years at mostly 16-20C storage. The B never dies.

A personal favourite long lived DIY single solution ready to be used in a tank with floating cover or stored in a bottle is one I call 777.
I have been flogged for calling it this, because it is not the exact same as commercial Harveys 777.

It works best if you regularly develop films, because it is used in a replnished manner, and likes to be 'fed' at least once a week to aminatina a constant level of developing energy.
The developing agents are metol, glycin (which is very resistant to aerial oxidation) and polyphenyldiamine (base). The alkali and preservative is sodium sulfite.
PPD is not the nicest developing agent for skin contact, and since the formula is replenished, wear gloves as well to keep the silver which builds up in the solution from depositing stains that get on you and darken thus staining your hands in a way that is only first visible the next day.

I have kept tanks of this 777 stuff going and working just fine for periods of over a year, when I am shooting enough to keep it happy and fed films to be developed regularly.
It too like to be worked at 24C, to keep processing times reasonable.

I hope this gives you ideas of what can work at elevated temperatures, and allows longer than average shelf lives.