Lazy during the night with the cuddle bag

He is fairly sociable so I don't see it as a "omg I'm scared I'll just stay here", I think it's just a matter of comfort/safety in his "home". But I wan't him to be active so he doesn't get fat (or sick) like one of the Insta hedgehogs, but on the other hand I don't want to stress him.

What's the temperature in the cage?

Usually 25 degrees Celsius during the day and 23 (sometimes 22) degrees Celsius during the night. But its been like this since I got him (9 months ago).

22C is too cool for him at night, and 23 may be pushing it as well, with it being warmer in the day. You want it to still be warm for him at night to keep him active - that's why he's staying in his snuggle bag, because it's warm and cozy. Getting a heating set up for his cage (lamp, ceramic heat emitter bulb, and thermostat), or a space heater for the room, or keeping your living space temperature higher at night should help.

The only option is a heat emitter with thermostat if I can find one here as I don't want to raise the living area temperature over 23 degrees (nor comfortable or healthy). I'll look for one. Thank's for the help !

If you can't find any near you, try amazon! They def have che's

I doubt Amazon delivers to Romania. If by a miracle they do, the delivery would be very expensive.

Amazon will ship certain supplies/items to Romania, so it might be worth checking if you absolutely cannot find what you need elsewhere.

After some research I can get a 100W ceramic heater bulb with the lamp and install my own thermostat (as I can't seem to find any specially made for terrariums that are under 85 euros) for about 60-70 euros total. The problem is I'm not sure this is worth it, as I just want the temperature to raise with 3 degrees Celsius in a 75 liter aquarium (transformed now in a terrarium). Another option is a 10/15W ceramic rock/tree heater with incorporated thermostat for about 15-25 euros which might do the job. Any thoughts on this ?

Ceramic heat rocks, heating pads, etc are not for use with hedgehogs. There have been many reports of hedgehogs being burned by such devices, and really, hedgehogs need the air temperature to be heated to within range.

A 100W ceramic heater bulb (Make sure the bulb's housing is rated for use with CHE's) with a thermostat attached would be your best bet.

A ceramic rock/tree heater won't heat the air so it's not going to work to keep the whole cage warm.

I know these things seem very expensive for the few degrees you want to raise the temp. I felt the same way after getting my CHE setup and spending $100 (I bought most of it after I had the hedgie so I had to buy quick and at a pet shop so very expensive) but it's for the safety and well being of your hedgie. Temperature fluctuations can send a hedgie into fatal hibernation. They need a consistent temperature of air in the cage, not just a hot and cold space like some animals. I bought my setup almost a year ago now (one hedgie passed quickly, this guy was younger) and they are still going strong and was a very worthwhile investment. Think of it as an investment in you hedgies lifespan and thus happiness for you and being assured you did all you could to take care of him/her!