You want to look at HTHS to evaluate "thickness". Valvoline and Mobil High Mileage are both Resource Conserving and no thicker than any other typical 10w30 with an HTHS of about 3.1. Pennzoil High Mileage is thicker at 3.3, so is Quaker State Defy 10w30 and Mobil 1 High Mileage (Full Synthetic not Super) is the thickest at 3.5 IIRC.
Unfortunately the trend the last few years has been to thin out High Mileage oils. Valvoline, Mobil and Castrol have all done it although Mobil has not messed with the Full Synthetic version. Castrol GTX High Mileage used to be the thickest High Mileage oil but no more.
Another "thick" 10w30 option is Rotella, Valvoline Premium Blue or Delo 10w30 HDEO's, all have an HTHS of 3.5.