You want tripels to finish pretty dry, so rather than adding extra malt or extract, I'd use less malt/extract and instead I'd use maybe 15-20% sugar (wouldn't go any higher than that though). Will boost the ABV and really help dry it out to where it should be. Candi syrup is great (adds subtle flavor), or just use corn sugar. Corn sugar is definitely going to be cheaper.
Doing extract, or AG? If you're doing AG, I'd mash low. My last tripel I did at 147.