Do you have a room set aside or do you just want to make an altar in one part of a room?
Do you want to have it so friends can come and pray with you - will you need seating? Will there maybe even be an opportunity to have a priest come to say Mass? (If so, chat with him about anything that I don’t cover below.)
It can be simple or complex, and scaled to fit your budget. You might look online at church supply companies - if you want a prie deux (kneeler). If you need seating for more than yourself, regular chairs would do, and church supply companies make chairs with kneelers.
You could also use cushions for kneeling.
Any table could make an altar, and you could have cloths of different colors for the liturgical seasons - white or gold for Easter & Christmas, purple for Lent & Advent, green for Ordinary Time, red for Pentecost and Martyrs, would be basic. If you get really into it you could also have rose/pink for Gaudete Sunday/Laetare Sunday, and blue for the Blessed Mother.
You could top this with a fancier lace or some kind of overlay to create a focal point.
Candles are good, of course, and the church supply companies offer options in the liturgical colors for these as well. The glass bottle candles or colored glass shells with plastic candle refills are sturdy and safe, and less mess than taper candles. Or smaller votive cups would also work. These could contain tealights for easy cleanup.
Then you can choose nice statues and/or pictures to aid in your devotions, and place them in a nice arrangement. Flowers are good, too, with vases or just laid at the feet of the statues, whichever works best.
If you have a nice big family Bible, you could get a Bible stand to place it on.
