1. Make sauce: Hull and slice berries. Mix 1 cup berries with lemon juice and 2 Tbsp. sugar in a large bowl. Using a fork, mash berries into a chunky pulp. Combine another 1 cup berries and 2 Tbsp. sugar in a small saucepan over medium heat. Cook, stirring, until the berries start to give off liquid, about 2 minutes. Increase heat to medium-high and cook, stirring often, until mixture is thick and pulpy, about 5 minutes longer. Stir cooked berries into mashed berries. Cool slightly.
2. Make filling: Put lemon curd in a large bowl. In a separate bowl, beat cream, yogurt and sugar with an electric mixer until stiff peaks form. Stir about a quarter of whipped cream mixture into lemon curd, then gently fold in remaining cream mixture.
3. Assemble trifle: Trim and discard both ends of cake. Cut cake crosswise into approximately 1/3-inch-thick slices. Spread each slice thinly with jam. Pour 1/2 cup lemon filling in bottom of a 14-cup trifle bowl or other large glass bowl. Spread evenly. Top with cake slices, jam sides up, trimming cake slices as necessary to make a flat layer. Pour about 1/2 cup strawberry sauce over, distributing fruit as evenly as possible over cake layer. Spread 1/3 of remaining sliced berries over sauce. Build two more layers with remaining filling, cake, sauce and sliced strawberries, arranging layers so they're even and visible through the bowl. Cover with plastic wrap and refrigerate for at least 6 hours or overnight.
4. Just before serving, whip 1 cup cream with an electric mixer until medium-firm peaks form. Spread whipped cream decoratively on top of trifle. Spoon into individual dessert bowls and serve immediately.