Deca only is a terrible first cycle.
Stick with what you have - 10 weeks of TE at 300mg/wk.
If you dont want DHT conversion, you may be better with a shorter ester than Enanthate. Long and short estered Testosterone's will all convert to estrogen (aromotase) to varied degrees.
If you want no conversion to DHT/E, then go with something like Tbol 40-60mg/ED for 6 weeks.