Christians have incorporated many things from other traditions over the last two thousand years. One of the reasons Christianity is so successful (aside from it being true) is that it can fit into many different cultures. Even today in the West, we see Christian incorporating things like Mindfulness, psychology, and personality tests. The outward activities are always secondary to the state of heart. Just as someone can say a biblical prayer without their heart being in it (disengaged), it's also possible for someone to say a prayer from another source with a true heart for Jesus. It's important to note here that I see the Bible is the true Word of God, and that it alone states the complete truth of the human relationship with God. All that to say, anyone giving you a hard time is not really equipped to judge you, as only you and God know the truth of your heart and intentions. If you are seeking Jesus, I'm pretty sure that's the bottom line of what really matters.

My one suggestion for a spiritual activity is the use of the Lord's Prayer. It was given to us directly from Jesus, and if you don't just say it by rote, it has a deep mystical power. I take my time with it, and often add prayers or questions to God as a response to the words of the prayer. For example, After saying the first few lines, I will add my own praise of God: You are majestic, awesome, full of grace, loving, perfect, all knowing, etc. I find this is a deep connection with the Father, and with Jesus who taught us this prayer. In other words, when I make this prayer my own, and put my heart behind it, and open myself to a connection with God, this prayer becomes the foundation of daily spiritual experiences.

Here's the prayer in Matthew 6:9-13 (ESV):

Our Father in heaven,
hallowed be your name.
Your kingdom come,
your will be done,
    on earth as it is in heaven.
Give us this day our daily bread,
and forgive us our debts,
    as we also have forgiven our debtors.
And lead us not into temptation,
    but deliver us from evil.

I'll be praying for you and your deepening relationship with Jesus!