Not so simple a choice
First, all furlers have pin to pin deduction that simply put is the amount deducted from the luff of a full hoist hank on sail, like a 150%, to fit onto a furler. For example, if a full hoist hank on 150% for a Catalina 25 has a luff of say about 28 feet and the particular furler one wishes to use has a pin to pin deduction of 20 inches, then the maximum luff of the furling headsail will be 26 feet 4 inches. This is a serious performance reduction.So, while it is true that a mast head rig like the Catalina 25 derives its power from the jib and as such replacing that sail first would be logical, I think you really need to get a good grasp on just how you intend to use your vessel. Furlers are lousy for racing and you may find yourself doing enough racing where you’ll really wish to have a high performance hank on tri radial headsail. However, with something like a Harken furler that has a removable drum, you can gain back most of the lost luff and use a non-furling race headsail with a luff tape that slides into the same groove as a furling sail. The result is you can both competitively race, yet still can have say a furling 135%. However, this is an expensive proposition.Further, checking forestay tension with a furler can be very difficult. If you have as much luff as you can get onto the furler, then to check forestay tension, you remove the forestay, remove the drum, remove the luff extrusion, put the turnbuckle and/or drum back on, put the forestay back on, check and adjust the forestay tension with a Loos gauge, try to put some marks to note the position or number of turns required on the turnbuckle, remove the forestay, remove the turnbuckle and/or drum, put the luff extrusion back on, put the drum and turnbuckle back on, adjust the turnbuckle to the afore determined position, and hope you got everything right. As an alternative, as I do, you can use a short luff on your furling headsail. This means the luff extrusion can be short enough where one raises it off the drum and before butting up against the swag at the top of the forestay wire expose about ten inches of forestay wire. This will allow a Loos gauge measurement. However, this does create a serious loss in headsail power. Take your pick. So, for now, do not decide new sails until you have had this boat for a while and can well establish your needs.As far as mainsails go, the best value is from Catalina Direct. Ullman makes their sails and for production sails are perfect for Catalinas. The full batten sails are best I think as they provide a really large roach and become just about the largest mainsail one puts onto a Catalina. And natch, lose footed is the way to go as well.With the incidentals like sail insignia and numbers put on that others charge for, I think you’ll find Catalina Direct sails an excellent bargain.