Biggar is set to miss the next two matches after being banned following his red card at Gloucester last weekend.
And Saints have opted to switch Furbank from full-back to 10, with James Grayson as cover on the bench.
Tommy Freeman moves from the wing to full-back, opening up a slot for Ollie Sleightholme to fill.
Rory Hutchinson and Matt Proctor continue at centre as Fraser Dingwall is still sidelined.
There are some key changes in the pack as Courtney Lawes, who suffered a thumb injury last weekend, and David Ribbans are ruled out.
Alex Coles replaces Ribbans in the second row, while Teimana Harrison comes in for Lawes.
Loosehead prop Manny Iyogun has recovered from injury and will be among the replacements at The Rec.
As for Bath, they make four changes to their side.
Miles Reid returns to the back row for the first time since captaining the blue, black and white to victory against Newcastle Falcons at the end of February.
Joining him in the pack is Mike Williams who locks down next to captain Charlie Ewels.
The front row remains consistent for the third game running, while Josh Bayliss and Taulupe retain their spots at blindside flanker and No.8 respectively.
In the backs, Danny Cipriani comes in for a start at fly-half, with Will Muir the other addition to the backline.
Wing Muir lines up in the back three alongside Semesa Rokoduguni and Tom de Glanville. The trio have 15 tries between them this season.
Ben Spencer is named as vice-captain from scrum-half.
Max Clark and Jonathan Joseph continue in the centre.
South African back row Jaco Coetzee is back in the 23 for the first time since the home win over Bristol Bears.
Bath: De Glanville; Rokoduguni, Joseph, Clark; Muir; Cipriani, Spencer; Morozov, Dunn, Stuart; Williams; Ewels (c); Bayliss, Reid, Faletau.
Replacements: Du Toit, Cordwell, Rae, Richards, Coetzee, Simpson, Bailey, Cokanasiga.
Saints: Freeman; Sleightholme, Proctor, Hutchinson, Collins; Furbank, Mitchell; Waller, Matavesi, Hill; Coles, Ratuniyarawa; Ludlam (c), Harrison, Augustus.
Replacements: Haywood, Iyogun, Carey, Moon, Nansen, James, Grayson, Francis.