A system for use with a bed having a frame and a supporting surface supported by the frame, the system comprising: a sheet having a bottom surface adapted to be placed above the supporting surface of the bed and a top surface opposite the bottom surface, wherein the sheet comprises: a first piece of sheet material at least partially formed of a first low-friction material having a first coefficient of friction, wherein the first piece of sheet material forms the bottom surface of the sheet; and a second piece of sheet material at least partially formed of a second high-friction material having a second coefficient of friction forming at least a part of the top surface of the sheet; wherein the first piece of sheet material is larger than the second piece of sheet material; wherein the second coefficient of friction is higher than the first coefficient of friction such that the top surface provides greater slipping resistance than the bottom surface; a tether strap connected to the sheet and extending from the sheet, the tether strap being configured for connection to the bed, wherein the tether strap comprises an elastic portion forming at least a portion of a length of the tether strap; and a wedge comprising a base wall, a ramp surface, and a back wall, the ramp surface being positioned at an angle to the base wall, wherein the wedge is configured to be positioned under the sheet such that the base wall confronts the supporting surface of the bed and the ramp surface confronts the bottom surface of the sheet. a sheet having a bottom surface adapted to be placed above the supporting surface of the bed and a top surface opposite the bottom surface, wherein the sheet comprises: a first piece of sheet material at least partially formed of a first low-friction material having a first coefficient of friction, wherein the first piece of sheet material forms the bottom surface of the sheet; and a second piece of sheet material at least partially formed of a second high-friction material having a second coefficient of friction forming at least a part of the top surface of the sheet; wherein the first piece of sheet material is larger than the second piece of sheet material; wherein the second coefficient of friction is higher than the first coefficient of friction such that the top surface provides greater slipping resistance than the bottom surface; a tether strap connected to the sheet and extending from the sheet, the tether strap being configured for connection to the bed, wherein the tether strap comprises an elastic portion forming at least a portion of a length of the tether strap; and a first piece of sheet material at least partially formed of a first low-friction material having a first coefficient of friction, wherein the first piece of sheet material forms the bottom surface of the sheet; and a second piece of sheet material at least partially formed of a second high-friction material having a second coefficient of friction forming at least a part of the top surface of the sheet; wherein the first piece of sheet material is larger than the second piece of sheet material; wherein the second coefficient of friction is higher than the first coefficient of friction such that the top surface provides greater slipping resistance than the bottom surface; a tether strap connected to the sheet and extending from the sheet, the tether strap being configured for connection to the bed, wherein the tether strap comprises an elastic portion forming at least a portion of a length of the tether strap; and a wedge comprising a base wall, a ramp surface, and a back wall, the ramp surface being positioned at an angle to the base wall, wherein the wedge is configured to be positioned under the sheet such that the base wall confronts the supporting surface of the bed and the ramp surface confronts the bottom surface of the sheet.