You camera isn't holding you back. I would think that slide film would be even harder for you to use since the time it takes to get feedback on your results will be measured, mostly likely, in days, not seconds.
I've photographed my gallery owner's (Katherine Baltivik) works for her to have printed so quality was of utmost importance. Here's what one looked like:
You'll need the following things:
- A good source of light that does not have glare. She has a west facing exterior wall on the gallery with a nice nail in for hanging pieces. If I shoot in the morning the sun does not directly shine on the piece.
- A tripod. Yes, this way you can set up the framing and then not worry about it. You can also shoot long exposures without worrying about shake.
- A DSLR where you can manually focus with a decent lens. If you don't have a lens that manually focuses, don't worry about it, just let it auto focus.
Position the camera as perpendicular to the artwork. Turn off auto-focus and then do whatever your camera needs to manually focus. For any modern Canon you'll go into live view mode then press the + button once. Now you are looking at 5x mag and you can get a coarse focus. Then press the button again to get 10x mag and do your final focus. On a Canon you can move the "joystick" around to move the focus box so you can position on a spot with good detail.
Then take the shot. Use RAW mode if you are comfortable with RAW processing. (And you should learn it, I use Adobe Lightroom and I'm stunned at how awesome it is. You can download a 30 day free trial.)
Why RAW? This lets you have great control over the sharpness of the image. With JPG you only get what the camera is set to give you. (There are other reasons to use RAW but they probably don't apply here.)
Now bring the image into Photoshop and do a perspective correction. Drag the 4 corners to the 4 corners of your artwork. This corrects for any errors that crept in because the artwork wasn't vertical or when the camera wasn't perpindicular.
Save the image and you're done!