Wrapping some insulation such as towels, (old) sleeping bag, moving blankets, etc. around the kettle's sides, bottom, and lid helps against heat loss during the mash.
Make sure to remove the insulation before heating on your stove.
Size your batches to your fermentation vessels, filling them only 3/4 to 4/5 with wort. Leaving 1/5-1/4 of the fermenter's volume as headspace is good practice. Some yeasts are also more vigorous than others, especially when fermenting at higher temps.
That said, fermenting toward a yeast's
lower end of her temp range is usually recommended, it makes better tasting beer. There are exceptions, such as Saison yeasts, and some Kveik yeasts, showing their character at the higher side of their temp range.