A focusing screen usually isn’t the best fix here. On the 1000D, the most accurate method is to use Live View on a tripod and magnify the image to check focus precisely. That will generally be more accurate than focusing through the viewfinder.

If you must use the viewfinder, the camera’s focus-confirmation indicator can help when turning the focus ring manually, though it may not be perfectly reliable.

If autofocus is failing because the scene is too dark, try using AF-assist illumination from the flash so the camera has enough contrast to lock focus.

Also consider that in low light, blur is often caused by camera shake or mirror slap rather than missed focus. A tripod, steadier technique, or avoiding very slow shutter speeds may help as much as any focusing aid.

So the usual solution is: use Live View magnification when possible, use focus confirmation as a backup, and treat a focusing screen as optional rather than necessary.