Updated: May 17
If your house is 75F with good natural lighting, you may not need to add heat at all. There's a difference however, between 75F with AC blasting and no light, VS a steady 75F with indirect sunlight. The latter is much more favorable.
Juvenile jumping spiders will need warmer and brighter conditions to eat well and grow well. I use a seeding heat mats with a thermostat set at 78 - 80F. NEVER use any heating source that can't be controlled with a thermostat and temperature probe to the precision of +/- 2 degrees. You do not want to overheat your spiders.
I do lower the temperatures to 74F or so during the winter, to provide a natural temperature dip. I take my adults off heat, as well, with room temperatures in the winter at about 67F, to slow their metabolism and prolong lifespan.
I have a window with indirect sunlight across from the spiders, as well as a lamp over my growing juveniles. My lamp and ceiling light are on a timer for about 12 hours of light per day.