Usually it is a candle, wood would more likely be used for the earth element.
Wood would be better to associate with element earth than fire.
If you are not able to obtain a candle or even light it. Use a fabric or paper that has the color red or orange. These colors are warm and passionate- like fire. You can even have a photograph or drawing of fire. Whatever works for you.
You can look up and or draw sigils for fire. You could also just have a picture of a fire. There's also electric candles if the problem is having actual candles.
If you can have candles, tea lights are really cheap and come with multiple ones.